Production apparatus for making green compact

ABSTRACT

An apparatus for producing a green compact includes a circuit that circulates die assemblies, each of which contains a rubber mold having rubber in at least its side portion. The apparatus also includes a high density filling device that has a feeder for feeding powder into the rubber molds; a pusher or a vibrator or both a vibrator and a pusher; a die press machine configured to impart a compaction force sufficient to produce the green compact to each of the circulating die assemblies in succession; and a device for removing the green compact from each rubber mold. The high-density filling device, the die-press machine and the removing device are successively arranged along the circuit. Each of the circulating die assemblies has sufficient structural integrity to withstand the compaction force because all structure necessary to withstand the compaction force is present in the circulating die assemblies.

This application is a continuation of U.S. application Ser. No.08/328,544, filed Oct. 25, 1994, which is a continuation of U.S.application Ser. No. 08/093,896, filed Jul. 20, 1993, both nowabandoned, which is a divisional of application Ser. No. 07/800,356,filed Dec. 2, 1991, now U.S. Pat. No. 5,250,255.

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing permanentmagnets and sintered compact. More particularly, the present inventionrelates to a method for compacting a permanent-magnet powder under amagnetic field while enhancing the anisotropic property and henceenhancing the magnetic properties of the permanent magnets so made. Theparticles of the powder as compacted are oriented in the easy directionof magnetization. The so-oriented particles are then subjected tocompacting and the particles are fixed by the compacting force. Thegreen compact is then sintered to obtain a sintered magnet.Alternatively, resin is impregnated into the so-oriented powder so as toobtain the resin-bonded magnet. The permanent-magnet (hereinafterreferred to as the "magnet") powder and resin may be compacted togetherto obtain the resin bonded magnet.

In addition, the present invention relates to a method for producing asintered compact by means of die-pressing a fine powder of an ordinarymaterial, i.e., a material other than a magnet material, under nomagnetic field and then sintering the green compact. More particularly,the conventional diepressing method is improved such that the finepowder is compacted. In the powder-metallurgy technique, not only thedensity of a sintered compact increases but also the grain size of asintered compact can be refined by lessening the particle diameter ofthe powder. As a result, sintered materials such as Al and Ti areconsiderably strengthened, and the magnetic properties of soft magneticferrous materials are enhanced. However, the flowability of fine powderis very poor. When the powder having poor flowability is filled in a dieunder gravity, the bridging phenomenon is very liable to occur in thedie, and the filling density greatly varies for each filling. The weightof each green compacts (hereinafter referred to as "unit weight") variesgreatly and the average filling density of the powder is lower.

The present invention is also related to a production apparatus of agreen compact, which is subjected to sintering, or to the production ofa magnet.

DESCRIPTION OF RELATED ARTS (Magnet)

Although CIP (cold isostatic pressing) is used for compacting magnetpowders, this method is not industrially carried out, because thecompacting process is complicated. That is, the magnet powder isoriented in a rubber mold under a magnetic field, then the rubber moldis immersed in a liquid medium, and the particles of the magnet powderare isostatically compacted in the liquid medium. The industrialcompacting method is the die-pressing method by means of a punch(es) anddie(s).

Conventional methods are the perpendicular die-pressing method, in whicha magnetic field is applied to the magnet-powder in a directionperpendicular to the moving direction of the punch(es), and the axialdie-pressing method, in which the magnetic field is applied parallel tothe moving direction of the punch(es).

The axial die-pressing method is used for forming a flat anisotropicmagnet, whose anisotropic direction is perpendicular to the majorsurface. The perpendicular die-pressing method is used for forming ananisotropic magnet having a relatively simple shape, whose length in themagnetically oriented direction is relatively large. Most of themagnets, particularly ferrite magnets, demanded in the market have sucha shape that the magnetically oriented direction is perpendicular to themajor surface.

It is generally recognized that the magnetic properties, particularly Brand (BH)_(max), of the sintered magnets industrially produced by theperpendicular die-pressing method are superior to those produced by theaxial die-pressing method. However, Japanese Examined (Kokoku) PatentPublication No. 55-26601 discloses that magnetic properties equivalentto those by the perpendicular die-pressing method can be obtained by theaxial die-pressing method using a rubber mold. In this method, themagnet powder is filled in a rubber mold, which has been preliminarilyset in the metal die of a die-press machine. The above-mentionedexamined patent publication describes that the magnetic properties ofthe ferrite magnet are impaired by the disclosed die-pressing methodusing a rubber mold.

There is also a wet die-pressing method which is usually carried out forcompacting the powder of ferrite magnet, because the magnetic powder isliable to orient in the slurry under the magnetic field, and, hence ahigher orientation is obtained than by orienting the dry powder.

In the wet die-pressing, a slurry with a water content of from 30 to 40wt % is injected into the die cavity via an aperture in the die wall. Afilter consisting of one or plurality of sheets or cloths is attached tothe upper punch provided with a suction channel. During compacting bythe upper and lower punches, the slurry in the die cavity is subjectedto vacuum suction and the water is sucked through the filter.

(Ordinary Materials)

Since the specific surface area of fine powders is great, they are soactive that they are oxidized in air and deteriorate in air.Particularly, the fine powder of Al--Li alloy and Ti alloy, whosereliability must be very high when they are used for the structuralparts of an aircraft, are readily oxidized in air and, in extreme case,spontaneously ignite. In addition, the fine powder is very pyrophoric.When the powder is seized between the die and punch of a die-pressmachine, the lubrication is lessened and the friction is increased,which can generate a spark which can ignite of the fine powder.

There is a limitation in the shape of a green compact which is compactedby the die-pressing method, which is one of the most frequently usedshaping methods of powder. Such green compacts having unevenness orgrooves, e.g., a screw, and a very elongated shape cannot be produced bydie-pressing.

It has been proposed to modify the isotropic compacting in thedie-pressing for example in Japanese Unexamined (Kokoku) PatentPublication No. 49-135,805. According to this proposal, a rubber mold isset in a die, and the powder is filled in the rubber mold. The powder istherefore compacted in a moving direction of a punch(es) and also in adirection perpendicular to the former direction. The compression istherefore pseudo-isotropic. The compacting described above mayhereinafter be referred to as the rubber mold die-pressing.

A rotary press-machine is known in the field of die-pressing of powder.This rotary press-machine is provided with a circular die having aplurality of die-cavities and the same number of punches as thedie-cavities. A feeder box for feeding the powder into the die-cavitiesis slidably mounted on the circular die. During the rotation of thecircular die, the die-cavities pass beneath the open bottom of thefeeder box, and, the powder falls under gravity into the die-cavity.When the circular die further rotates, the bottom end of the side wallof the feeder box is displaced relative to the circular die and the diecavities, where the powder is filled, while rubbing them by such end.The punches are secured to a punch holder, whose position relative tothe circular die is fixed. The punch holder therefore rotates togetherwith the rotation of the circular die. The punches are held by the punchholder in such a manner that they can be advanced from the punch holdertoward the die cavities. Driving mechanisms for the punches, such as acam and rail, are mounted within the punch holder, and drivesuccessively the punches when pressing the powder. Each punch istherefore pushed into each die-cavity in the sequence determied by thedriving mechanisms.

SUMMARY OF THE INVENTION (Magnets)

Since the powder of rare-earth cobalt magnet is filled into the rubbermold, which is preliminarily set in the die of die-press machine,according to the method of the above-mentioned Japanese Examined PatentPublication No. 55-26601, the powder is naturally filled or filled undergravity in the rubber mold. In this case, the apparent density of thepowder of rare-earth cobalt magnet in the mold is approximately 18% ofthe density of the rare-earth cobalt alloy itself. As is known, themagnetic orientation of the powder is very sensitive to its density, andthe magnetic orientation of powder filled at a higher density than thenaturally filled density is difficult. It is therefore conventionallycarried out to fill the magnet powder by means of a shaker or the likeinto a die cavity, so that the magnet powder has the naturally filleddensity in the die cavity.

The present inventors tested the method disclosed in Japanese ExaminedPublication No. 55-26601 not only with regard to the rare-earth cobaltmagnet but also for the ferrite and neodymium magnets and made thefollowing discoveries. When the naturally filled powder is compacted toproduce a green compact having an apparent density of approximately 50%,the green compact cracks in the die-press machine or the rubber moldnon-uniformly deforms during the die-shaping. In this case, the greencompact so non-uniformly deforms that its shape cannot be adjusted bymodifying the shape of the rubber mold.

The powders of the magnet are crushed considerably finer, and hence haveconsiderably poorer flowability than those of the ordinary materials, inorder to fully extract the magnetic properties thereof. Although aconsiderable amount of lubricant can be added to the powder of ordinarymaterials so as to improve their flowability, the amount of lubricant isextremely small even if it is added to the magnet powder, because theremaining carbon and the like have a detrimental effect upon themagnetic properties of the magnet powder. A small amount of thelubricant is not at all effective for improving the flowability of themagnet powder. In addition, it is possible to enhance the flowability ofthe ordinary materials by increasing the particle diameter. This measureis not utilized for the magnet powder, as the magnetic propertiesdecrease. Because of the reasons as described above, the density of thenaturally filled powders is as low as 18% or less for the rare-earthcobalt magnet and 16% or less for the ferrite magnet.

It is therefore an object (hereinafter referred to as "the firstobject") of the present invention to provide a production method for amagnet, by which the orientation of a green compact is enhanced and themagnetic properties are improved by utilizing the elasticity of therubber mold, without causing cracks, crazing and fracture of the greencompact.

Heretofore, as it has been necessary in the die-pressing and orientingmethod under magnetic field to synchronously apply the magnetic fieldand compacting pressure to the magnet powder, the process control ismore complicated than in the case of a mere die-pressing withoutapplication of magnetic field.

It is therefore another object (hereinafter referred to as "the secondobject") of the present invention to provide a production method foranisotropic magnets which does not cause cracks, crazing and fracture ofthe green compact, and by means of simply controlling the compactingstep and magnetic field-application step. It is a specific aspect of thesecond object to enhance the orientation of the anisotropic magnet to alevel higher than that attained by the conventional method.

Japanese Examined Patent Publication No. 55-26601 mentioned above statesthat the rubber mold replaces the pressure medium used in CIP. Therubber mold therefore completely surrounds the magnetic powder toisostatically apply pressure to the magnet powder. Such rubber moldtherefore cannot be utilized for the wet die-pressing.

It is therefore a further object (hereinafter referred to as "the thirdobject") of the present invention to provide a wet die-pressing methodfor producing a magnet, by which the orientation of a green compact isenhanced and the magnetic properties are improved by utilizing theelasticity of the rubber mold, and, further, by which a green compact isproduced without cracks, crazing or fracture.

In the method disclosed in Japanese Examined Patent Publication No.55-26601, since the rubber mold is preliminarily placed in a die-pressmachine and the magnet powder is then filled into the rubber mold, thepunch, columns for guiding the vertical movement of the punch, and thelike impede the feeder which feeds the magnet powder into the rubbermold. The disclosed method has therefore a low efficiency. In addition,until one cycle consisting of the powder-feeding, shaping, and removalof a green compact is completed, the next cycle cannot be initiated.This method is therefore inappropriate for continuous production of alarge number of magnets.

(Ordinary Materials)

It is yet another object (hereinafter referred to as the fourth object)of the present invention to provide a sintering method for producing asintered compact having a density of 90% or more, in which a fine powderof the ordinary material can be compacted without using organiclubricant. It is one aspect of the fourth object that the fine powder ofsoft material, such as aluminum and its alloys, is compacted to a greencompact having high and uniform density. It is also an aspect of thefourth object that the sintered compacts can be produced at anefficiency as high as the conventional die-pressing. It is a furtheraspect of the fourth object to provide a sintered compact having a highdensity and low content of impurities, such as carbon, which aredetrimental to the properties of metals, particularly Ti. It is anotheraspect of the fourth object to provide a highly densified sinteredcompact of hard material, whose density can be only enhanced in theconventional method by means of post-sintering working, such as sizing,rolling and drawing.

The conventional rotary-press machine can fill the powder only at anatural density.

It is therefore an object (hereinafter referred to as the fifth object)of the present invention to provide a die-press apparatus, which canfill the powder at a density higher than the natural density.

It is yet another object (hereinafter referred to as "the fifth object")of the present invention to provide an apparatus for producing asintered compact, which is appropriate for continuous production.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) through (C) illustrate incidence of cracks during compactingof a rubber mold and powder filled in the rubber mold.

FIGS. 2(A) through (D) illustrate a method for filling the powder in arubber mold.

FIGS. 3(A) through (D) illustrate a preliminary compacting method ofpowder.

FIGS. 4 through 12 illustrate several embodiments of filling the powderat high density.

FIGS. 13 through 15 illustrate embodiments of a rubber mold.

FIG. 16 illustrates a defect, the so-called "elephant leg" of the greencompact.

FIGS. 17 through 23 illustrate embodiments of a rubber mold.

FIG. 24 illustrates dimensions of a rubber mold.

FIG. 25 illustrates a dry die-press apparatus.

FIGS. 26(A) through (D) illustrate several embodiments of a back-upplate.

FIG. 27 is a schematic top view of a circulating type-dry die-pressapparatus according to the present invention.

FIG. 28 is a partial cross sectional view of the apparatus shown in FIG.27.

FIGS. 29(A) through (F) illustrate the movement of a cam plate used inthe apparatus shown in FIGS. 27 and 28.

FIGS. 30(A) through (C) illustrate a method of die-pressing the magnetpowder in a rubber mold under inert-gas atmosphere.

FIG. 31 is a schematic top view of another circulating type-drydie-press apparatus according to the present invention.

FIG. 32 illustrates the movement of a linear transporter used in theapparatus shown in FIG. 31.

FIG. 33 illustrates a wet-type die-press apparatus according to thepresent invention.

FIG. 34 is a partial view of another wet-type die-press apparatusaccording to the present invention.

FIG. 35 illustrates the movement or energization of the parts of theapparatus shown in FIG. 33.

FIG. 36 illustrates an embodiment of a rubber mold used in the wetdie-pressing.

FIG. 37 illustrates an embodiment of the apparatus for fluidizing andfilling the slurry in a rubber mold located in a reduced-pressureatmosphere.

FIGS. 38(A) through (C) illustrate a pre-compacting method of slurry.

FIG. 39 is a top view of a circulating type-wet die-press apparatusaccording to the present invention.

FIGS. 40 and 41 illustrate several embodiments of a rubber mold forproducing a hollow green compact.

FIG. 42 illustrates how cracks are generated in a green compact formedby a rubber mold.

FIG. 43 illustrates the dimensions of a rubber mold.

FIGS. 44(A) through (L) illustrate various combinations of materials andportions of a rubber mold.

FIG. 45 illustrates the rubber mold used in the Examples.

FIG. 46 is a schematic cross sectional view of a palette and a movablestage.

FIG. 47 is a drawing showing a rail carrying the palette.

FIG. 48 is a drawing showing a linear arrangements of the devices forproducing a green compact.

FIG. 49 is a elevational view of an embodiment of the magnetproduction-apparatus using palettes and quadrilateral transferringpassage.

FIGS. 50 and 51 illustrate a means for transporting the palette.

FIG. 52 is a drawing of a guide frame.

FIG. 53 illustrates a method for weighing the powder.

FIG. 54 is a drawing of a rubber mold for forming a screw.

FIGS. 55(A) and (B) illustrate the rubber molds consisting of separableparts.

FIGS. 56 and 57 illustrate a method for expanding a rubber mold.

FIG. 58 illustrates laminar cracks.

FIG. 59 illustrates a method for producing a rubber mold.

FIG. 60 is a drawing of the rubber mold used in Example 18.

FIG. 61 is a drawing of the rubber mold used in Example 20.

FIG. 62 is a drawing of the rubber mold used in Example 21.

FIG. 63 is a drawing of the rubber mold used in Example 22.

FIGS. 64(A), (B) and (C) are drawings of the rubber mold used in Example23.

FIGS. 65(A), (B) and (C) are drawings of the rubber mold used in Example24.

DETAILED DESCRIPTION OF THE INVENTION Means for Preventing Cracks in aGreen Compact Shaped by Using Rubber Mold

FIG. 1 illustrates a flat green compact of magnet powder shaped in arubber mold by a die-press machine.

When the magnet powder is rare-earth cobalt powder, the density of thenaturally filled powder in a rubber mold is from approximately 11 to 13%in most cases. The powder is then compacted so that the dimensiondecrease is from 30 to 40% and hence is great. During deformation of therubber mold 10 as shown in FIG. 1(C), frictional force is generatedbetween the portions 10s, 10k and 10u as well as between the rubber mold10 and the metal dies (not shown). Among the deformations, thenon-uniform deformation dy is generated in the cover 10u and the bottom10k and promotes the generation of cracks 5d which extend parallel tothe pressing direction of the punch. On the other hand, the non-uniformdeformation dx is generated in the side portion of the rubber mold andpromotes the generation of cracks 5e which extend in a directionperpendicular to the pressing direction of the punch. The non-uniformdeformation dx results in a serious deformation, the so-called"elephant-leg", on the edge of the green compact.

When the magnet powder is compacted and oriented under a magnetic fieldand is then demagnetized insufficiently, the magnetization remains in agreen compact, with the result that stress is generated in the greencompact due to the static magnetic energy. Therefore, even if the cracksgenerated in a green compact are very small, the cracks are rapidlyenlarged due to the stress mentioned, thereby breaking the green compactinto fragments. Particularly, when the edge of a green compact deformsto form the elephant leg, cracks due to the remaining magnetization arevery likely to occur. In order to prevent the non-uniform deformation ofa green compact in a rubber mold and cracks and the like, the powdermust be filled in a rubber mold at a higher density than the naturaldensity. Since the powder filled at a high density undergoes a smallerdeformation than by the ordinary compacting method under magnetic field,the non-uniform deformation of the rubber mold is lessened, therebypreventing cracks and shape-failure of a green compact. The orientationis therefore high notwithstanding the high-density filling in a rubbermold, because the orientation of magnet powder is improved by thedeformation of the rubber mold in a direction perpendicular to themoving direction of the punch(es), and also by preliminarily applyingthe magnetic field to the magnet powder prior to the compacting step.

Aspects of Invention

The high density of magnet powder or mixture of magnet and resin powdersfilled in a rubber mold according to the present invention means thatthe density is at least 1.2 times the natural filling density,regardless of the kind of magnet and resin materials. The naturallyfilled density depends mainly upon the particle diameter of the magnetand resin powder.

The density of natural filling is the apparent density of the powderfilled in a rubber mold under gravity. The method for measuring apparentdensity stipulated in the Japan Industrial Standard is a standard methodfor measuring the density of natural filling. However, the valueobtained by this method is considerably remote from the density usuallyattained by the feeder box, or the measurement is impossible in extremecases because the flowability of the magnet powder is very poor.According to the present invention, the density of natural filling ismeasured by filling the powder from the powder pan 90 shown in FIG. 2(A)until the top of the powder arrives at the upper frame 100 whichprevents the powder 5 from overflowing from the rubber mold 10. Theposition of the powder pan 90 is such that the distance between thebottom end of the powder pan 90 and the bottom of the rubber mold 10 is3.7 times the depth of the cavity of the rubber mold 10.

The natural filling density is 14% for the rare-earth cobalt magnets(including R--Co and R--Fe--B) having a particle diameter of from 3 to 4μm, and 12% for the ferrite magnet having a particle diameter ofapproximately 0.7 μm. The high density of the rare-earth magnet attainedby this invention and ferrite magnet is therefore at least 16.8% and14.4%, respectively. The high filling density is preferably from 25% ormore for rare-earth-iron-boron magnets and rare-earth cobalt magnets.The density is more preferably 29% or more both for rare-earth magnetsand ferrite magnets. When the filling density exceeds 50%, theorientation becomes impossible under the ordinary intensity of magneticfield. The filling density is preferably 50% or less.

The rubber mold used according to the present invention has a bottom andconsists of rubber at least in the side portions thereof. Such a rubbermold is hereinafter simply referred to as the rubber mold. The bottom ofthe rubber mold may be integrated with the other portions of the rubbermold. The lower punch or the bottom of a lower-closed die may constitutethe bottom of the rubber mold. The rubber mold according to the presentinvention may be provided with a detachable cover consisting of metal orrubber. In this case, the cover is included in the rubber mold herein.The rubber mold may be provided with a plurality of cavities, so that aplurality of green compacts is produced at once.

In accordance with the first object of the present invention, there isprovided a production method for a magnet, comprising a compacting stepof magnet powder under magnetic field, characterized by: filling at ahigh density the magnet powder in a rubber mold outside a die-pressmachine by at least one means consisting of imparting vibration theretoand pressing the same with a pusher, or by preliminarily compacting themagnet powder and then inserting the preliminary compacted magnet powderinto a rubber mold outside a die-press machine; setting the rubber moldin the die-press machine, into which the magnet powder is filled; andcompacting the rubber mold and the magnet powder by a punch(es) of thedie-press machine thereby obtaining a green compact of the magnetpowder. The concept of "outside the die-press machine" herein indicatesthat the rubber mold is in a position shifted from the axial position ofthe punch(es) of a die-press machine but does not indicate that therubber mold must be completely outside a die-press machine consisting ofa punch(es), dies, a die-holder, a ram and the like.

In accordance with the first object of the present invention, there isalso provided a production method for a magnet according to theabove-described inventive method, further comprising the steps of:covering the upper open part of the rubber mold with a cover; and,subsequently, prior to the compacting step in the die-press machine,applying instantaneous magnetic field or applying the stronger staticmagnetic field than in the compacting step, to the magnet powder in therubber mold.

In accordance with the second object of the present invention, there isprovided a production method for a magnet comprising a compacting stepof a magnet powder, characterized by: filling the magnet powder at ahigh density in a rubber mold outside a die-press machine by at leastone means consisting of imparting vibration thereto and pressing thesame with a pusher, or by preliminarily compacting the magnet powder andthen feeding the preliminary compact of magnet powder into a rubber moldoutside a die-press machine; covering the upper open part of rubber moldwith a cover; prior to the compacting step in the die-press machine,applying an instantaneous magnetic field or a applying stronger staticfield to the magnet powder in the rubber mold than in the compactingstep; setting the rubber mold in the die-press machine, into which themagnet powder is filled or compacted; and compacting the rubber mold andthe magnet powder by a punch(es) of the die-press machine, withoutapplication of magnetic field, thereby obtaining a green compact of themagnet powder.

In accordance with the third object, there is provided a productionmethod (hereinafter referred to as "the third method") of a magnet,wherein the magnet powder is compacted by a die-press machine providedwith an upper punch, a filter and a water-suction channel formed in theupper punch, so as to shape the slurry in magnetic field, characterizedby: filling the slurry into a rubber mold in or outside the die-pressmachine; setting the rubber mold in the die-press machine; setting thefilter between the upper punch and the open upper portion of the rubbermold; and compacting the rubber mold and the slurry thereby sucking thewater or solvent of the slurry through the filter and the water-suctionchannel. In accordance with the first and second object of the presentinvention, there is provided a method (hereinafter referred to as "thefourth method"), characterized by repeatedly carrying out, in a circuit,the steps of: filling the magnet powder in a rubber mold at a highdensity outside the die-press machine; applying magnetic field to themagnet powder according to the first or second method; die-pressing;and, removing the mold from the die press machine.

The rubber used for the rubber mold is not limited but may be naturalrubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber,isobutylene rubber, ethylene-propylene rubber, butadiene-acrylonitrilerubber, chloroprene rubber, isobutylene-isoprene rubber,ethylene-propylene rubber, ethylene-propylene rubber, chlorosulfonatedpolyethylene rubber, polysulfide rubber, silicone rubber, fluorinatedrubber, urethane rubber, polyurethane rubber, epichlorohydrin rubber,acryl rubber, ethylene-vinyl acetate rubber, polyester rubber,chlorinated butyl rubber, chlorosuofonated polyethylene rubber,chlorinated polyethylene rubber, poly-isoprene rubber, norbornenepolymer, and the like.

Plastics and wooden material, which do not completely plastically deformunder the pressure of a punch, may be used. They are for exampleurethane, silicone resin, melamine resin, unsaturated polyester resin,epoxy resin, diallyl phthalate resin, polyimide, polyethylen,polypropyrene, polystyrene, AS resin, AbS resin, polyvinyl chloride,polyvinylidene chloride, polyamide, polymethyl methacrylate,polycarbonate, polyacetal, polysuofonate, fluorine resin, celluloseacetate, and the like. Plasticizer may be added to the plastics.

In accordance with the fourth object, there is provided a productionmethod (hereinafter referred to as the "fourth method") for a sinteredcompact having a density of 90% or more, comprising: preparing a rubbermold which consists of rubber at least in a side portion thereof;filling fine powder of a material other than magnet material, havingaverage particle size of 50 μm or less and being essentially free oforganic binder at a density at least 1.15 times the natural densitydefined below, in the rubber mold located outside the die-press machine;locating in the die-press machine the rubber mold, into which the finepowder is filled; compacting the rubber mold and the fine powder by apunch(es) of the die-press machine thereby obtaining a green compact;and sintering the green compact. The natural density is measured byfilling the fine powder into the rubber mold from a powder pan until thetop of the fine powder arrives at an upper frame which prevents the finepowder from the rubber mold, and a position of the top of the powder issuch that distance between the bottom end of the powder pan and thebottom of the rubber mold is 3.7 times the depth of cavity of the rubbermold.

In accordance with the fifth object, there are provided the followingproduction apparatus:

(a) An apparatus for production of a green compact comprising: a circuitfor circulating rubber molds; a high-density filling device comprising afeeder of the powder into the rubber molds which comprise rubber atleast in their side portions, and a pusher; a die-press machine; and, adevice for removing a green compact from each rubber mold, saidhighdensity filling device, die-press machine and removing device beingsuccessively arranged along the circuit.

(b) An apparatus for production of a green compact comprising: a circuitfor circulating rubber molds which comprise rubber at least in theirside portions; high-density filling device comprising a feeder forfeeding powder into the rubber molds and a vibrator along with orinstead of said pusher at the same place as said feeder; a diepressmachine; and, a device for removing a green compact from each rubbermold, said high-density filling device, die-press machine and removingdevice being successively arranged along the circuit.

(c) An apparatus for production of a green compact, comprising: acircuit for circulating rubber molds which comprise rubber at least intheir said portions; high-density filling device comprising a loader ofa preliminarily compacted powder into the rubber molds and a pusher; adie-press machine; and, a device for removing a green compact from eachrubber mold, said high-density filling device, magnetic-field generator,die-press machine and removing device being successively arranged alongthe circuit.

(d) An apparatus for production of a green compact, comprising: acircuit for circulating rubber molds which comprise rubber at least intheir said portions; feeder of slurry of magnet powder into the rubbermolds; a magnetic-field generator: a die-press machine; and, a devicefor removing a green compact from each rubber mold, said feeder, saidmagnetic-field generator, die-press machine and removing device beingsuccessively arranged along the circuit.

(e) An apparatus for production of a green compact, comprising: acircuit, for circulating rubber molds which comprise rubber at least intheir side portions; a loader of preliminarily compacted slurry into therubber molds; a magnetic-field generator; a die-press machine; and, adevice for removing a green compact from each rubber mold, said loader,said magnetic-field generator, die-press machine, and said removingdevice being successively arranged along the circuit.

(f) An apparatus for production of a green compact, comprising: acircuit for circulating rubber molds which comprise rubber at least intheir side portions; a feeder of a slurry of magnet powder into therubber molds; magnetic-field generator; a die-press machine; a devicefor removing a green compact from each rubber mold, and, a means fordegassing treatment of the inside of the cavity of the rubber molds,said feeder, said magnetic-field generator, die-press machine, removingdevice and degassing means being successively arranged along thecircuit.

(g) An apparatus for production of a green compact, comprising: acircuit for circulating rubber molds which comprise rubber at least intheir side portions; a loader of preliminarily compacted slurry into therubber molds, degassing means for degassing treatment of the innersurfaces of the rubber molds; said magnetic-field generator, die-pressmachine, removing device and said degassing means being successivelyarranged along the circuit.

(h) An apparatus for production of a green comact, comprising: a circuitfor circulating rubber molds which comprise rubber at least in theirside portions; a feeder of a slurry of magnet powder into the rubbermolds: a means for degassing treatment of the inner surfaces of therubber molds; a magnetic-field genertor: a die-press machine; a devicefor removing a green compact from each rubber mold; said feeder, saiddegassing means, said magnetic-field generator, die-press machine, areremoving device being successively arranged along the circuit.

(i) An apparatus for production of a green compact, comprising: acircuit for circulating rubber molds which comprise rubber at least intheir side portions; a loader for circulating rubber molds, as well as:a loader of preliminarily compacted slurry into the rubber molds; amagnetic-field generator; a die-press machine; a device for removing agreen compact from each rubber mold; and a means for degassing treatmentof the inner surfaces of the rubber molds, said loader, saidmagnetic-field generator, die-press machine, said removing device, andsaid degassing means being successively arranged along the circuit.

(j) A production apparatus of magnet, wherein a high-density fillingdevice comprising a feeder for feeding magnet powder into a rubber moldwhich comprises rubber at least in a side portion thereof, and one orboth of a pusher and a vibrator, die-press machine, and a device forremoving a green compact are separately located on a straight passage,and, a rail is provided along said straight passage and mounts areciprocating means thereon, and, further a palette, on which the rubbermold is detachably mounted, is reciprocated by said reciprocating meanson the rail along said passage.

(k) An apparatus for production of a green compact comprising: amold-supporting means having a configuration of an equilateral orscalene polygon; a high-density filling device comprising a feeder ofthe powder into the rubber molds which comprise rubber at least in theirside portions and a pusher; a die-press machine; and, a device forremoving a green compact from each rubber mold; said high-densityfilling device, die-press machine and removing device being located ateither an apex region or side region of said polygon, or both regions,said apparatus further comprising a means for transporting the rubbermold in a linear movement between the adjacent apexes.

(l) An apparatus for production of a green compact, comprising: a moldsupporting means having a configuration of equilateral or scalenepolygon and rubber molds which comprise rubber at least in their sideportions; a high-density filling device comprising a feeder for feedingpowder into the rubber molds and a vibrator along with or instead of apusher at the same place as said feeder; a die-press machine; and, adevice for removing a green compact from each rubber mold; saidhigh-density filling device, die-press machine and removing device beinglocated at either an apex region or side region of said polygon, or bothregions, said apparatus further comprising a means for transporting therubber molds in a linear movement between the adjacent apexes.

(m) An apparatus for production of a green compact, comprising: a moldsupporting means having a configuration of equilateral or scalenepolygon as well as: a high-density filling device comprising a feeder ofpowder into rubber molds which comprise rubber at least in their sideportions; a vibrator and a pusher; a die-press machine; and, a devicefor removing a green compact from each rubber mold, said high-densityfilling device, die-press machine and removing device being located ateither an apex region or side region of said polygon, or both regions,said apparatus further comprising a means for transporting the rubbermolds in a linear movement between the adjacent apexes.

(n) An apparatus for production of a green compact, comprising: a moldsupporting means having a configuration of equilateral or scalenepolygon as well as: a high-density filling device comprising a feeder ofpowder into rubber molds which comprise rubber at least in their sideportions, a vibrator and a pusher; a die-press machine; and, a devicefor removing a green compact from each rubber mold, said high-densityfilling device, die-press machine and removing device being located ateither an apex region or side region of said polygon, or both regions,said apparatus further comprising a means for transporting the rubbermold in a linear movement between the adjacent apexes.

First and Fourth Methods

Referring to FIG. 2, the powder 5 which may be magnet powder or a powderof ordinary materials, is filled at a high density by impartingvibration thereto. The powder 5, whose weight has been preliminarilymeasured, is naturally filled into the rubber mold 10 by flowing it downfrom the powder pan 90 (FIG. 2(A)). The powder 5 stacks higher than theupper surface of the rubber mold 10 up to the interior of the guideframe 100 fixed to the upper surface of the rubber mold 10. The rubbermold 10 is subsequently placed on the vibrator 41 which impartsvibration to the rubber mold during or after the powderfeeding FIG.2(B)). The vibrator 41 may be of a magnetic-type or a crank-type and maygenerate horizontal or vertical vibration. The vibration frequency isnot limited but is, for example, from 1 to 60 Hz.

Pusher 121 forces down the powder 5 rising above the upper surface ofthe rubber mold 10, until the upper surface of the powder 5 is loweredto the same level as the upper surface of the rubber mold 10 (FIG.2(C)). The pusher 121 and the guide frame 100 are then lifted above therubber mold 10 (FIG. 2(D)).

In the present invention, not the (uncompacted) powder but thepreliminarily compacted powder may be subjected to the compacting by adie-press machine. The preliminary compacting to a high density iscarried out by using a pressing device, such as a die-press machine. Theattained density of a preliminarily compacted powder is preferably from25 to 50% in the case of rare-earth magnets and from 20 to 50% in thecase of ferrite magnets.

Referring to FIG. 3, a pre-compacting device comprises a die 125, a diebottom 126 consisting of a movable bottom plate, and a punch 128. Thepowder 5, which has been preliminarily weighed, is naturally filled intothe die cavity by means of flowing it down from the powder pan 90 (FIG.3(A)). The powder 5 is then compacted under the pressure in the range offrom 15 to 100 kg/cm² (FIG. 3(B)). The rubber mold 10 is thentransferred beneath the pre-compacting device, the bottom 126 is pulledaway from the die 125, and the punch 128 is further pushed down (FIG.3(D)). The pre-compact 129 then falls down into the rubber mold 10. Thepre-compact is preferably smaller than the inner dimension of the rubbermold 10, because the magnetic-field pulse can be effectively applied tothe pre-compact 129.

The filling at high density as illustrated in FIGS. 2 and 3 is carriedout outside a die press-machine because the rubber mold with filledpowder can be immediately compacted, as soon as it is loaded in themachine, thereby enhancing productivity. A die (not shown in FIGS. 2 and3) may be integrally connected with the rubber mold 10. In this case thedie and the rubber mold 10 with the filled powder are set together in adie-press machine.

According to an embodiment of the method for filling illustrated in FIG.4, a feeder box 206 is slidably located directly on the die 2. Thepowder 204 falls from the feeder box 206 into the rubber mold 200 viathe open top of the rubber mold 200. During the dropping of the powder204, it is stirred by the stirrer 213. The stirrer 213 consists ofrotary blades 213 secured around a shaft, and is installed within thefeeder box 206, thereby eliminating the bridging of the powder 204stacking at the open top of the feeder box 206 and hence smoothlydropping such powder into the rubber mold 200.

According to another embodiment illustrated in FIG. 5, the rotary blades212 consist of blades 213 rotating around a horizontal plane. The O-ring215 is fitted on the top part of the feeder box 206 and clearancebetween the shaft 215 and the feeder box 206 is gas-tightly sealed.

FIG. 6 illustrates another embodiment of the feeding method with thesame reference numerals for the parts which are the same as shown inFIG. 4. The stirrer 212 consists of the blades 216 and pusher rod 217which is secured to the blades, so that the wide surfaces of the blades216 can move horizontally along the longitudinal direction of the feederbox 206. The bottom edges of the blades 216 are curved to enhance thestirring efficiency. When each blade 216 passes over the die cavity ofthe rubber mold 200, the powder 204 is forced downwards by the verticalcomponent of the force applied from the blade to the powder 204. Theblades 216 may not only consist of plates as shown in FIG. 6(B) but mayconsist of frames 216' as shown in FIG. 6(C) or consist of rotary blades(not shown).

FIG. 7 illustrates an embodiment in which instead of the stirrer asshown in FIG. 4 through 6, a vibrator 218 is installed within the feederbox 204 so as to apply directly the vibration to the powder 204. Thevibrator 218 may be attached to the outer surface of the feeder box 206so as to vibrate the feeder box 206 and then indirectly the powder 204.

Referring to an embodiment illustrated in FIG. 8, the powder 204 is fedon the upper side of the conveyor 223 wound around the wheels 222 and isthen converted to the layer along with the circulating movement of theconveyor 223. A vibrator 218 is brought into contact with the lower sideof the conveyor 223 and imparts the vibration to the powder 204 beingconveyed, thus enhancing its density. The powder having high density isdropped from the end of the conveyor 223.

Referring to an embodiment illustrated in FIG. 9, a screw rod 225,around which blades 226 are spirally secured, is mounted coaxially inthe container 227. When the screw rod 225 is rotated anti-clockwise, thepowder 204 is stirred in the container 227, caught between the blades226 and fed into the direction of the outlet 227a of the container 227.Since the flowability of the magnet powder is poor and, further, thefriction between the powder particles and between the powder and innerwall of the container is great, the powder moves more slowly than therotation of the blades 226. The powder far behind each blade moves morerapidly than the powder directly behind each blade, forcing it to pushinto the latter powder due to the rotation of blades. The powder ispressed also due to the principle of reaction which is in the oppositedirection to the movement of the powder. In the embodiment shown in FIG.9, the density of the powder is enhanced due to both the stirring andthe principle of reaction.

Referring to FIG. 10, the parts which are the same as those shown inFIG. 8 are denoted with the same reference numerals. The powder 204 ispressed between a pair of rolls 228 to enhance its density, and is thendropped into the rubber mold 200.

Although not shown in the drawings, the powder may be pressed in a metaldie or by rolls to form a compact in the form of a sheet, which is thencrushed to form granules. Such granules may be filled in the rubbermold.

The powder subjected to the processes as illustrated in FIGS. 4 through10, may be preliminarily subjected to degassing so as to enhancedensity.

According to an embodiment illustrated in FIG. 11, the powder is filledunder gravity as well as magnetic field generated by the electromagneticcoils 230. The magnetic field having an intensity of preferably from 0.1to 1 T attracts the powder into the bottom of the rubber mold 200 toenhance the density.

According to an embodiment illustrated in FIG. 12, the electromagnets231 are placed beneath the rubber mold 200 so as to generate thegradient magnetic field in the rubber mold 200 and hence the force F ina direction perpendicular to the gradient, attracting the powder intothe bottom of the rubber mold 200. Instead of the electromagnets 231,permanent magnets generating a flux of intensity from 0.1 to 3 T may beused.

The rubber mold must be a continuous body or comprise continuouslyconnected sections. In the latter case, the rubber mold may be aseparable type as shown in FIG. 13, although the friction at thepartition surfaces of the mold-sections 10a, 10b is not favorable.Furthermore, as shown in FIG. 14, portions 10c of a rubber mold 10 notin direct contact with the powder 5 may consist of granular, liquid, gelor powdery rubber, although such a structure of the rubber mold 10 isunfavorably complicated. The punches and the die of a die-press machineare denoted in FIG. 14 by reference numerals 1a, 1b and 2, respectively.Referring to FIG. 15, water, oil, or liquid rubber is filled in the diecavity 10e formed within the rubber mold 10. This would contribute tocreating a compacting force as uniform as possible which is applied tothe powder 5.

Referring to FIG. 17, the cylindrical side portion 10b of the rubbermold 10b is tapered (10f) at the inner, upper and lower edges. Thistaper 10f is preferable for preventing the elephant legs 5a, 5b shown inFIG. 16 from occurring. The cover and bottom of the rubber mold aredenoted by 12 and 10k, respectively. Instead of the taper 10f, a curvededge may be formed to prevent a crack of green compact on the edge.

In the production of the most ordinary, disc type anisotropic magnet, arubber mold located in the die cavity is in contact with the innerperipheral wall of the die. The compacting force of a punch is convertedby the rubber mold to a radial compacting force directed inwards. Therubber mold must smoothly slide on the inner peripheral wall of the dieand be thoroughly compacted in order to generate strong compactingforce. It is therefore preferable to apply a lubricant or anti-abrasivematerial between the rubber mold and die.

The lubricant, such as BN (boron nitride), may be applied on the innerwall of the rubber mold to lessen the adherence of the powder on therubber and hence to prevent the cracks in a green compact due to theadherence. In addition, a thin rubber film may cover the inner surfaceof the rubber mold. This rubber film relieves inner stress of a greencompact which is generated when a punch is lifted up and which may causecracks in a green compact.

The static magnetic field is applied to the green compact of magnetpowder being compacted and is in the range of from 8 to 12 kOe, as inthe conventional method. After the compacting step under magnetic field,demagnetization is carried out as in the conventional method.

Preferred compacting conditions are now described by using the followingparameters.

Compacting ratio A₁ : compacting ratio of powder in the directionperpendicular to the moving direction of a punch(es), i.e., the decreasein the cross-sectional area of green compact due to compacting dividedby the cross-sectional area of the green compact before deformation bythe punch.

Compacting ratio S₀ : compacting ratio in the moving direction of apunch(es), i.e., the dimensional decrease in the moving direction of apunch(es) divided by the dimension of powder before deformation by thepunch(es). The dimension in this context is the average dimension in thedirection of punch motion.

(1) Axial Die-Pressing Preferably 0<A₁ ≦6S₀, more preferably 0.4S₀ <A₁≦4S₀, most preferably S₀ <A₁ ≦3.6S₀.

When A₁ is virtually zero, the magnetic properties are not at allimproved. 0<A₁ <0.4S₀ is such a range that the magnetic properties arenot improved outstandingly but an ultra-thin green compact or a greencompact having an irregular shape can be produced. The magneticproperties are outstandingly improved at 0.4S₀ <A₁, preferably 4S₀ <A₁.However, at A₁ >6S₀, the compacting pressure becomes impractically high.

Theoretically, the compacting condition 0<A₁ is always fulfilled,provided that the thickness of the rubber mold in the moving directionof a punch(es) is not zero but a finite value. However, if suchthickness is very small, the rubber mold buckles and cannot shape thegreen compact during the pressing. The thickness of the rubber mold inthe moving direction of a punch(es) should therefore be selectedappropriately considering the elastic ratio of rubber so as not to incurbuckling and to realize the preferable A₁.

(2) Perpendicular Die-Pressing

0<A₁ ≦4S₀, more preferably 0<A₁ ≦3S₀, most preferably 0<A₁ ≦2.4S₀.

Since a clearance is formed between the rubber mold and a compact inperpendicular die-pressing, the friction between the green compact andthe rubber mold is small when the green compact is removed from therubber mold. It is therefore possible to produce an irregular-shapedcompact or an ultra-thin compact, whose production is impossible byconventional die-pressing. Similarly, as in the axial die-pressing,thickness of a rubber mold should be selected so as not to causebuckling of the rubber mold and to attain such a preferable value of A₁as not to increase the required pressing pressure to an excessivelygreat value.

The preferable value of A₁ for obtaining outstanding improvement of themagnetic properties is lower than that of the axial die-pressing.

The pressure applied through a punch(es) is preferably in a range offrom 50 to 5000 kg/cm², more preferably in a range of from 100 to 1000kg/cm². These ranges partially overlap with those of the conventionaldie-pressing. But their low level is lower than the conventional rangesbecause of entire circumference of the powder is compacted due to theuse of a rubber mold, which easily promotes densifying of a greencompact.

The size of magnet is not at all limited. The magnet may range from anultra-small-sized one, such as the rotor magnet of a wrist-watch and therotor of an electronic cylinder lock, to a small-sized magnet, such asan ultra-thin magnet used in an OA (Office Automation) machine, astepping motor-magnet, the direct-current motor of a video camera, andthe actuator of a robot, and to a large-sized magnet used in an MRI(magnetic resonance image) apparatus.

An arc-shaped segment magnet can also be produced by the method of thepresent invention as is illustrated in FIGS. 18 and 19, which show anelevational view and a cross-sectional view of a rubber mold. The upperand lower punches (not shown) have the same concave and convex surfacesas the upper and lower surfaces of the arc-shaped green compact,respectively.

A prismoid can be produced by using a rubber mold 10 shown in FIG. 20. Arectangular compact having an arc-shaped top surface can be produced byusing a rubber mold 10 shown in FIG. 21. A frustum of pyramid can beproduced by using a rubber mold 10 shown in FIG. 22. A green compacthaving a flat sheet-shape with a groove through the center can beproduced by using a rubber mold 10 shown in FIG. 23.

A rubber mold for producing a green compact having a complicated shapecan be designed by computer simulation for shaping such a complicatedshape while using the dimension data of green compacts which areproduced by using rubber molds with a similar but simpler shape than thecomplicated shape.

The following described method, which is a simple designing method,enables to estimate the approximate shape of a rubber mold when a greencompact has a simple shape and the outer shapes of the green compact andthe rubber mold are the same.

The simplified designing of a rubber mold is based on these premises:the volume of the rubber mold is unchanged before and after thecompression (premise 1); and the ratio of apparent density ofun-compacted magnetic powder to the apparent density of a green compactis constant (premise 2).

When a rubber mold 10 consists of an annular mold 10s and is used forshaping a disc-shaped green compact 11 as is shown in FIG. 24, thefollowing formula exists according to premise 1.

    yπ{(x.sub.0 /2).sup.2 -(x.sub.1 /2).sup. }=Y.sub.G π{(x.sub.0 /2).sup.2 -(1.sub.G /2).sup.2 }                           (1)

Premise 2 is realized for the dry and ungranulated ferrite-powder to beapproximately 1.9:1. The following equation is therefore obtained.

    yπ(x.sub.1 /2).sup.2 :Y.sub.G (1.sub.G /2).sup.2 =1.9:1 (2)

The approximate dimension of the side portion 10s of a rubber mold canbe designed based on the above two equations. The design and trialproduction are repeated several times, so as to modify the dimension ofthe side portion 10s in order to allow easy removal of the green compactfrom the rubber mold, and to enhance dimension accuracy of the greencompact. In this modification, deformation of the rubber mold andhardness of the rubber are also taken into consideration.

The die-press machine used in the present invention may be a hydraulicor a mechanical one. All types of die-press machines from a small-sizedmanual one to an automatic type can be used in the present invention.Preferred die-press machines are a twin-punch type machine, in which theupper and lower cylinders move and compact simultaneously, or adie-float type machine and a withdrawal type machine, in which only oneof the upper or lower cylinders moves but the die moves synchronously tothe movement of the cylinder.

Preferred Embodiments of First Method

The orientation of a magnet, which is generally defined by Br/4 πIs(Br--residual flux density, 4 πIs--saturation flux density), is improvedby the first method as described above.

Now, a preferred embodiment of the first method is described. When themagnet powder is filled in a rubber mold at a considerably high density,particularly 29% or more, the friction force between the powderparticles is greater as the filled density is higher. It is thereforedifficult to provide by the static field amounting to 8 to 12 kOe usedin the ordinary die-pressing under magnetic field a satisfactoryrotational force for overcoming the friction of the powder particles andhence to orient the powder particles. The orientation of magnet powdertends therefore to be lowered. According to a preferred embodiment ofthe first method, an instantaneous magnetic field is applied to themagnet powder in the rubber mold prior to the die-pressing in magneticfield. Alternatively, a stronger static field than that of thedie-pressing under magnetic field is applied to the magnetic powder inthe rubber mold, prior to die-pressing under magnetic field. Thepreliminarily applied magnetic field generates a rotational force whichis sufficient for re-orientation of the magnet powder. The magnet powderfilled in a rubber mold is set in a die-press machine and is magnetizedunder pulse or static field. Extremely high orientation is attained bythis magnetization with good reproducibility, notwithstanding anextremely high filling density as high as 29% or more.

Rotational force preferably imparts impact to the magnetic powder beingpreliminarily magnetized, so as to enhance the orientation degreethereof. The magnetic field having intensity of from 5 to 10 kOe,particularly 10 kOe or more, more particularly 15 kOe or more, isimparted to the magnet powder at least once, preferably twice or more.The intensity of pulse magnetic field must change greatly at the initialstage. When the specified intensity of the magnetic field is attained,it may keep a constant value or may decrease gradually.

If the magnet powder is filled in a rubber mold at very high density,there are local differences in density of the powder in the mold. Ifsuch powder is compacted without preliminary application of magneticfield, locally non-uniform deformation of a compact may occur. If agreen compact has such a shape that cracks are liable to occur, thelocal difference in the density easily cause cracks and crazing of thegreen compact or deformation of the sintered compact. The deformedsintered compact must be machined at a great machining cost. Theabove-described drawbacks resulting from the very high density can besolved by the preliminary application of the magnetic field to themagnet powder, because the agglomerated powder particles aredisintegrated and uniformized thereby.

The preliminary compact can also be treated by the preliminaryapplication of the magnetic field as described above and canadvantageously attain very high density without causing cracks or thelike in a green compact.

FIG. 25 illustrates an apparatus for preliminary application of magneticfield and die-pressing under magnetic field. The right part of thedrawing illustrates a line for filling the magnet powder in a rubbermold and loading it in a die-press machine. The electro-magnetic coil,which generates pulse, and disintegrates and orients the agglomeratedpowder particles outside the die-press machine, is denoted by referencenumeral 4a. The conveyor is denoted by 40. The vibrator 41 is inslidable contact with the conveyor 40 at its rear surface. The vibratormay be in slidable contact with the conveyor 40 at its side surface. Thefeeder 42 feeds magnetic powder into a rubber mold 10i provided with abottom (hereinafter referred to as "the rubber mold 10i"). The feedingis carried out by pouring the powder 5 when the conveyor 40 stops.Simultaneously with the feeding of the powder, the rubber mold 10i isshaken by the vibrator 41 to enhance the filling density of the powder.When the conveyor 40 rotates in the direction shown by the arrow, therubber mold 10i is moved upto the position where a cover 10h isattached, where the conveyor 40 again stops. A piston rod 53 driven bythe hydraulic cylinder 52 is pushed down to tightly insert the cover 10hinto the rubber mold 10. The conveyor 40 then again rotates to move therubber mold 10i provided with the cover 10h (hereinafter referred to as"the rubber mold 10h,i") to an intermediate position between themagnetic field coils 4a, 4a, which then impart the magnetic field-pulseto the powder 5. A pusher (not shown) pushes the rubber mold 10h,i, inwhich the oriented magnet-powder is contained, so that it slides on theconveyor 40 and the table 44, which is located on the same level as theupper portion of a die 2, toward the die 2. The time necessary for theabove-described series of movements is as follows.

(a) Pouring from the feeder 42: 0.5-30 seconds

(b) Vibration: 1-30 seconds

(c) Rotation of the conveyor (from the feeder 42 to the hydrauliccylinder 52): 1-10 seconds

(d) Inserting of a cover 10h: 1-30 seconds

(e) Rotation of the conveyor (from the hydraulic cylinder 52 to theposition of the magnetic coils 4a, 4a): 1-10 seconds

(f) Imparting of the magnetic-field pulse: 1-10 seconds

(g) Rotation of the conveyor (from the position of the magnetic coils4a, 4a to the die 2): 1-10 seconds

The control unit 50 controls the time-sequence and duration of theabove-mentioned series of operations (a) through (g). More specifically,the control unit 50 generates such a command that: the conveyor 40 doesnot rotate during the operations (a), (b), (c) and (d); and, further,these operations are initiated when the conveyor 40 stops. In addition,operations (c), (e) and (g) must occur synchronously with each other.Since operation (f) can be the shortest and operation (b) can be thelongest in the above-described case, the conveyor rotation according to(c) does not begin even if (b) is completed, until completion of (f).The control unit 50 also commands such holding and starting of theoperations as described above.

The control unit 50 also commands the rotation of a motor 51 forrotating a screw rod (not shown) in the feeder. When the screw rodrotates at a specified revolution per minute, the powder is caughtbetween the clearances of the screw and is fed into the rubber mold 10iin an amount which is specified by the total revolution of screw. Thecontrol unit 50 specifies the power, and energization-sequence and timeof the power source 55 for applying the magnetic-field pulse to thepowder.

Upon transmitting the end signal of the powder feeding from the motor51, this signal is input in the control unit 50. One of the conditionsfor moving the conveyor is thus fulfilled. Upon inputting the endsignals from operations 41, 54 and 55 to the control unit 50, all of theconditions for moving the conveyor are fulfilled. The conveyor 40 movesin the direction of the arrow for a specified distance and then stops.

The conveyor 40 may consist of a plurality of metal chains or beltsarranged successively in the conveying direction. An electro-magneticswitch or a dielectric sensor is provided at each clearance between themetal chains or the like. When the electro-magnetic switch or the likedetects mechanically or physically a rubber mold 10h,i, the signal isgenerated from the electro-magnetic switch or the like to stop theconveyor 40. The rubber molds 10h, i can be accurately stopped at aspecified position.

After die-pressing, the rubber mold 10h, i is lifted up by means of thelower punch 1b and is then transferred away from the die-press machinein a direction perpendicular to the drawing.

Preferred Embodiments of Fourth Method

The fine powder of ordinary materials has preferably an average particlediameter of 50 μm or less, more preferably 30 μm or less, furthermorepreferably 20 μm or less. The obtained sintered green compact can have adensity of 95% or more based on the true theoretical density of theordinary materials. The ordinary materials do not include magnet powderbut may be such metals as Fe, Co, Ni, Cu, Mo, Al, Mg and Ti, and theiralloys as well as compounds such as TiC and WC. The Fe or Fe based finepowder is prepared in most cases by atomizing the material with water orinert gas, and is occasionally provided in the form of carbonyl iron.The Al or Al-based fine powder is prepared by gas-atomizing ormelt-quenching. The Ti or Ti-based fine powder is prepared in most casesby repeated hydrogen adsorption and dehydrogenation. Mechanically milledfine powder may also be used. Such hard fine-powders as Fe--Co and Tialloy-powder, whose compactibility is poor, can advantageously becompacted by the fourth method without adding a binder or lubricant. Inaddition, since the rubber mold prevents the direct contact of the finepowder with a die, the fine powder is not seized by the die. As aresult, the lubricant need not be used at all. However, the binder in anamount of 1% by weight or less can be used, provided that the remainingcarbon does not exert a detrimental influence upon the properties of asintered compact.

When the fine powder is filled in a rubber mold under gravity, thedifference in the density of the filled powder locally varies. Inaddition, the green compact may crack as is described with reference toFIGS. 1(A) through (C). It is therefore necessary to fill the finepowder at a high density, i.e., at least 1.15 times the natural densitydescribed with reference to FIG. 2(A). The filling density is preferably1.3 times when the green compact has an elongated shape or greatunevenesses. When the fine powder is filled in a rubber mold, it shouldnot be so seriously deformed that a desired shape of green compact isnot obtained. This may occur at an extremely high-density filling, forexample more than 60% of the true density.

As is shown in FIG. 52, the bottom of the guide frame 100 may have sucha shape that it is virtually coincident with the top shape of the rubbermold 10. The top of the guide frame 100 may be somewhat expanded tofacilitate the powder feeding.

When a conventional shaker-type feeder is used for feeding the finepowder into a rubber mold through a guide frame, the filled weight offine powder greatly varies because of its poor flowability. It istherefore preferred to preliminarily weigh the fine powder to provide apredetermined weight and then charge the fine powder thus weighed into arubber mold. In this embodiment, the unit weight of green compacts canbe controlled very accurately. In addition, when such green compacts aresintered, the shrinkage ratio is constant, because the fine powderexhibits a constant shrinkage ratio. The green compacts having net shapecan therefore be stably produced.

Referring to the method illustrated in FIG. 53, the fine powder 5 isconveyed by the conveyor 302 and is fallen from the conveyor 302 ontothe vibrating mesh 303. The agglomerated particles of the fine powder305 are disintegrated by the vibrating mesh 303 and therefore do notfall in the form of lumps. The weighing instrument 306, positioned belowthe vibrating mesh 303, is provided with a container 304 which receivesthe fine powder 305. The weight of the fine powder 305 stacked on thecontainer 304 is monitored to collect a predetermined amount of the finepowder 5.

During a stopping period of the vibrating mesh 305, the fine powder 5virtually does not fall through the vibrating mesh 305. It is thereforepossible by means of repeating ON and OFF of the vibration of thevibrating mesh 305 to very accurately control the dropping amount of thefine powder 5 into the container 304. Instead of measuring the weight,the volume of the fine powder may be measured. In addition, instead ofthe container 304, a rubber mold or a rubber mold provided with a guideframe may be located on the weighing instrument so as to weigh and fillthe fine powder.

When the load from a punch(es) is relieved, a rubber mold restores itsshape. The green compact can therefore be removed from the rubber mold.However, when the filling density of the fine powder in a rubber mold isvery high, or when the green compact is somewhat uneven, the clearancebetween the green compact and the die may not be sufficient enabling theremoval of a green compact. In order to enable the withdrawal of a greencompact in such cases as above, a rubber mold may consists of separatedside parts 10a, 10b as shown in FIG. 54. Two or more parts of a rubbermold 10 may be divided when removing a green compact 320 from a rubbermold 10. Furthermore, the rubber mold 10 may have a cut plane 311 at aportion of the side wall.

When a green compact is withdrawn from the rubber mold 10, it isenlarged at the cut plane 311 so as facilitate withdrawal. In addition,the side portions 10a, 10b and the bottom 10c may be divided from eachother. It is however to be noted that the rubber molds shown in FIGS. 54and 55 have the following disadvantages. The fine powder may be seizedat the cut plane 311 or the divided parts of the molds. Furthermore, therubber mold may be twisted during the compacting, resulting innon-uniform deformation of the green compact. The setting time of theserubber molds in a die is long.

In order to eliminate the disadvantages as described above, theclearance between the green compact and the die is preferably enlargedwhen the green compact is withdrawn from the rubber mold. The enlargingof the clearance can be carried out by means of applying pressure of,for example, gas to the inner surface of the rubber mold, and/orreducing the pressure of the outer surface of the rubber mold. By thesemeasures, a pressure difference between the inner and outer surfaces ofa rubber mold is created to enlarge the clearance.

Referring to FIG. 56, a cylindrical cover 312 is rigidly attached to thetop of a rubber mold 310 having bottom. The rubber mold 310 and thecylindrical cover 312 are sealed therebetween. Pressurized gas havingpressure of from 1 to 5 atmosphere is admitted into the cylindricalcover 312 so as to expand the rubber mold. A suction pipe 314, which isprotruded in the rubber mold 310, is lowered so that the front end ofthe suction pipe 310 is pressed against the top of the green compact320. The green compact is then sucked by the suction pipe 314. When thegreen compact is a magnetic body, it may be attracted by anelectro-magnet.

Referring to FIG. 57, the pressure applied to the outer surface of arubber mold is reduced. A sealing cover 314 is pressed on the die 1 viathe O rings 315b. The rubber mold 310 is pressed upwards on the sealingcover 314 by the lower punch 308. An O ring 308 is fitted around thelower punch 308 and between the lower punch 308 and the die 1.Therefore, when the gas is evacuated through the gas-evacuation channel314a, the vacuum space 318 is created around the outer surface of therubber mold 310. The rubber mold 310 therefore expands to enlarge theclearance between the rubber mold 310 and the green compact 320. Theelectro-magnet 317 attracts then the green compact 310.

After die-pressing, a rubber mold may be turned upside down, and theclearance between a green compact and the rubber mold may be created toallow the green compact to fall out of the rubber mold.

The Second Method

In the second method, the preliminary application of magnetic field iscarried out as described hereinabove and the die-pressing of powder orpre-compact filled at a high density is carried out under no magneticfield. The apparatus for carrying out the second method is the one shownin FIG. 25, in which the magnetic coils 4 and power source 55 areomitted or modified so that they only generate a low magnetic field anddemagnetize the green compact. This apparatus has a simple constructionin the case the parts 4 and 55 are omitted. The efficiency is highbecause the magnetic field is not applied during the compacting in adie-press machine, thereby shortening the pressing time. Thedemagnetization may be omitted, when the remaining magnetization doesnot cause cracking and the like of a green compact. The omission istherefore determined taking the shape and dimension of the green compactinto consideration. The feature "no field" in the second method meansthat no provision for orienting, such as a coil, is used, but also meansthat the powder may be exposed to unavoidable magnetic field, such asthe leakage flux from a pulse-magnetic field generator adjacent to thedie-press machine, or geomagnetism.

The preliminary application of a magnetic field causes the orientationof powder and enables, without application of magnetic field duringdie-pressing, to attain the magnetic properties of a green compact asgood as in the conventional axial die-pressing. This may be sufficientfor several applications. In the present invention, the compacting ofpowder in a direction perpendicular to the moving direction of a punchis realized and does not cause buckling of the powder particles, withthe result that the preliminary orientation is not disordered by themovement of a punch. Contrary to this, when the die-pressing is carriedout in the die-cavity without a rubber mold, the pressure of the punchis directed to the same direction as the orientation direction of thepowder particles. In this case, buckling of the powder particles occurs,thereby disordering the orientation. In the present invention, thedirection of the powder particles parallel to the moving direction of apunch is essentially maintained due to the effect of the rubber mold asdescribed above. Incidentally, when the magnetic field is applied to thepowder being compacted in a die-press machine (the first method), goodorientation is stably obtained with very slight variance of theorientation.

The description hereinafter can be applied both to the first, second andfourth methods, unless otherwise mentioned.

Back-up Plate

The back-up plate is elastic material, which is harder than the rubbermold, and is located between the rubber mold and one or both of theupper and lower punch(es).

Referring to FIG. 26, several embodiments of the back-up plate areillustrated.

When a rubber mold 10 located in a die 2 is directly pressed by thepunches 1a and 1b, the rubber plastically flows into the clearancesbetween the die 2 and punches 2a, 2b (FIG. 26(A)), particularly when therubber is soft. The rubber is therefore caught in the clearances. Thewithdrawing of the punches 1a, 1b from the die 2 therefore becomesdifficult. In addition, the rubber mold 10 may be damaged. A back-upplate 12, which consists of harder elastic material than the rubbermold, is therefore located between the upper punch 1a and the rubbermold 10, and another back-up plate 12 is located between the lower punch1b and the rubber mold 10. The back-up plates 12 are elasticallydeformed by the pressing by the punches 1a, 1b and seal the clearancesbetween the punches 1a, 1b and die 2. A back-up plate 12 may be providedonly between the upper punch la and the rubber mold 10. In addition, asshown in FIG. 26(C), a recess may be formed on the edge of each punch1a, 1b to attach there an annular back-up plate 12. Furthermore, asshown in FIG. 26(D), the back-up plates 12 may be attached to therecesses formed around the edges of a rubber mold 10. When the pressingpressure is very high, the back-up plate is preferably chamfered on theedges which face the punch and die, to prevent plastic flow of theback-up plate in the clearance between the die and punch(es). Thechamfered surface may be concave, convex, straight or "L" shaped.

Circulating Type Apparatus

Referring to FIGS. 27 and 28, an embodiment of the apparatus accordingto the invention is illustrated by the top view and the side andpartially cross-sectional view.

In this embodiment, the die is embodied as a rotary disc type-die with aplurality of cylindrical through-holes (hereinafter referred to as the"dies"). Only two through-holes are shown but there may be three ormore. The motor 91 rotates the rotary die 2a so that the dies movearound the circular passage. The upper and lower punches 1a, 1b areinserted into each die from above and below, respectively, at positionP₁. The rubber mold 10s together with powder is filled into each die atposition P₂, where the mold loader 70 is set. A rubber mold 10containing a green compact is removed from the rotary die 2a at positionP₃, where the removers 78, 84 are set. The rotary die 2a is rotated bythe motor 91 so that each die passes through the positions P₂, P₁ andP₃, successively.

The rotary die 2a need not be totally made of expensive die steels butonly at the contacting portions with the punches. Plastics, iron and thelike can be used for the non-contacting portions so as to reduce theweight and cost of the rotary die 2a. The mold loader 70 is driven bytwo cylinders 71 and 80. The cylinder 70 reciprocates a hollow rod 79,on whose front end a suction piece is attached. A rubber mold 10 isloaded in the die 2 as shown in FIG. 28. The cylinder 70 is secured tothe piston rod 82 of cylinder 80 and is therefore lifted or lowered as awhole by the cylinder 80. When the cylinder 70 is in a lifted positionas shown by the dotted line, a rubber mold 10 is sucked by the suctionpiece above the conveyer. While the cylinder 70 stays in the liftedposition, the piston 79 advances up to a position above the die 2. Thecylinder 71 is then lowered to position the rubber mold 10 into the die2. The hydraulic units 76 and 81 drive the cylinders 70 and 80,respectively.

While the rotary die 2a rotates, the stationary cam 75 guides theliftable bottom 2d which is inserted in the die 2. The movement of theliftable bottom 2d is determined by the upper surface-profile of thestationary cam 75 as illustrated in FIG. 29. First, during thedie-pressing, the die is completely remote from the stationary cam 75(FIG. 29(A)). The liftable bottom 2d then rides on the skirt portion ofthe stationary cam 75 (FIG. 29(B)) and further rises along the slantedsurface (FIGS. 29(C) and (D)). When the liftable bottom 2d arrives atthe flat top of the stationary cam 75, the rubber mold 10, in which agreen compact has been compacted, arrives at the same level as the uppersurface of the rotary die 2a. At this moment, the rubber mold 10 is inthe position P₃ (FIG. 28). The liftable bottom 2d then lowers to openthe die cavity, where uncompacted powder can again be loaded.

As shown in FIG. 27, a conveyor 40, whose end is in the vicinity ofposition P₂, conveys the rubber molds in which the powder is filled. Apowder-feeder 42, a cover-mounting device 89 and a magnetic-pulsegenerator, e.g., the electromagnetic coils 4a, are provided at thedifferent positions of the conveyor 40, as shown in FIG. 27.

A second conveyor 140 is provided at such a position that its end is inthe vicinity of the position P₃. Along with the rotary movement ofrotary disc 2a, the rubber molds 10 are guided along the removing plate78 and slide on the stationary table 84, so that the rubber molds 10 aretransferred to the second conveyor 140.

Powder-filling in Inert Atmosphere

The powder of rare-earth magnets is preferably filled or loaded into arubber mold in an inert atmosphere, thereby preventing oxidation of thepowder during the filling or loading. In this embodiment, the methodsillustrated in FIGS. 2 and 3 are carried out in chamber 95 (FIG. 30)filled with inert gas as shown in FIG. 30. A cover 10h is tightly fittedon the rubber mold 10 in the inert gas atmosphere. The rubber mold 10 isthen set in a die-press machine as shown in FIG. 36(B). Afterdie-pressing, the rubber mold 10 is removed from the die-press machineas shown in FIG. 30(C). The method illustrated in FIG. 30 isadvantageously applied for rare-earth alloy powders crushed by a jetmill and in a non-oxygen atmosphere, for example, a nitrogen atmospherehaving oxygen content of less than the limit detectable by analysis.Such powder has an extremely low oxygen content so that the magnetproduced using such powder exhibits excellent magnetic properties. Thepowder is, however, extremely active so that it is readily flammable inair. Its handling is therefore difficult. The method illustrated in FIG.30 can extract the excellent magnetic properties from the highly activepowder as described, while enhancing the magnetic properties due to thecompacting in a rubber mold.

The green compact produced by the above-described methods are sinteredby the known method, and is then heat-treated, if necessary, so as toproduce a sintered magnet. The magnet powder and resin may be compactedtogether to produce a resin-bonded magnet.

Method and Apparatus using Circuit

FIG. 31 illustrates an embodiment of the fourth method. In thisembodiment, a rubber mold 10i consists of a cylindrical body without abottom. Its bottom is, however, closed with the rotary die 2a. A portionof the rotary die 2a therefore constitutes the bottom of the rubbermold. While the rubber molds 10i move successively along the circularpassage along with the rotation of rotary die 2a, the powder is fed by afeeder 42 into each rubber mold 10i; the filling density of the powderis enhanced by vibration and compacting by a pusher; a cover 10u (notshown in FIG.31 but shown in FIG. 32) is inserted at position C, themagnetic field is applied by means of the electromagnetic coils 4a toorient the powder; die-pressing by the die-pressing apparatus is carriedout with or without the application of magnetic field; the cover 10u isremoved at position F; and the green compact is removed by the removingdevice 62.

The removed cover 10u is returned by the linear transporter 140 (FIG.32) to its inserting position C. The linear transporter 140 comprises arail which guides the suction piece 140a which is in turn connected to asuction pump. A motor (not shown) is movably mounted on the rail anddisplaces the suction piece 140a to which the cover 10u is secured.

The removing device 62 comprises an arm 64, such as an electromagnet,capable of swivelling around the shaft 65 at a specified angle. When theelectromagnet is energized and is swivelled, the magneticallyanisotropic green compact is attracted to the arm 64 positioned abovethe conveyor 40. The arm 64 performs such a movement that it isswivelled back toward the position above the other conveyor 66 and isthen de-energized. The green compact is therefore placed on the conveyor66.

Since the rubber mold reverts to its initial shape after the compacting,an annular clearance 10r is formed around the green compact and betweenit and the rubber mold. The annular clearance 10r is sufficiently largeto allow removal of the green compact from the rubber mold by themagnetic attraction.

The conveyor 66 is driven by a step motor 67 which is controlled by thecontrol unit 50. This control unit 50 controls the above-describedoperation of the electromagnet 64 as well as the conveyor 66, i.e., theintermittent movement upon the placing of a green compact on it.

In FIG. 31, a cleaning device consisting parts 150-153 is provided.These are an air-piston 150, an air-unit 151, an electromagnet 152, anda power source 153 for energizing the electromagnet 152. When a greencompact is removed from the rubber mold, the electromagnet 152 isdisplaced above the rubber mold and is then energized by the powersource 153. The powder remaining in the rubber mold is attracted by theelectromagnet 152 thus cleaning the rubber mold.

According to the method as illustrated in FIG. 31, the die-press machine60 carries out only the compacting with or without the application ofmagnet field, that is, neither setting nor removal of a rubber mold arecarried out in the die-pressing machine 60. This method is thereforemore efficient than the method where die-pressing and setting andremoval of a rubber mold are all carried out in the die-press machine.One pressing cycle is therefore short in the former method. Theapparatus as shown in FIG. 31 is appropriate for large-scale production.

When the endless-type die-pressing method as illustrated in FIG. 31 isused for large-scale production of magnets, the time required forrespective steps may be as follows.

(a) Powder feeding, vibration, pushing (at position A) and movement upto step (b): 15 seconds

(b) Attachment of cover (at position C): 5 seconds

(c) Application of magnetic-field pulse (at position D): 15 seconds

(d) Die-pressing (at position E): 15 seconds

(e) Removal of cover (at position F): 5 seconds

(f) Removal of a green compact and cleaning of a rubber mold (atposition G): 10 seconds

Since the longest operation takes 15 seconds, and, further, theconveying time from each of the steps (a) through (f) to the next stepis 2 seconds, the time period for producing one green compact is 17seconds.

Next is described the time required for the respective steps of theconventional die-pressing method, in which the powder is filled into thedie-cavity of a die-press machine.

(a) Powder feeding by a feeder: 10 seconds

(b) Lowering of an upper punch (the lower punch shunts when feeding thepowder, and then lowers from the shunting position into the die): 5seconds.

(c) Pressing (application of static magnetic field, compacting by theupper and lower punches, and application of inverse magnetic field): 27seconds.

(d) Adjusting of shunting: 5 seconds

(e) Removal of a green compact: 10 seconds

The total time of the steps (a) through (e) is 57 seconds. The firststep (a) cannot be initiated for the next compact until all of the steps(a) through (e) are finished for the previous compact. Therefore, aslong as 57 seconds is necessary for producing one green compact.

Preferred Embodiments in view of Properties of Magnets

In the present invention, the powder is preferably fed into a rubbermold and is filled at a high density at the same place. If thepowder-feeding by a guide frame 100 is carried out at a different placefrom the high densification place by a pusher or the like, the guideplate must be transferred from the former position to the latterposition. As a result, the number of the guide plates requiredincreases, and hence the structure of the pressing apparatus iscomplicated.

The powder should not be fed directly from the feeder into a rubber moldbut should be fed via a mesh and another container; that is, the powderis first fed to the mesh, which sieves the aggregates of powder, andthen is fed to another container. After accurately weighing the powder,it is fed from the container into a rubber mold. Since the flowabilityof the magnet powder is very poor, it is difficult to feed an accurateamount of the powder from the feeder into the rubber mold. The method offeeding the powder via the mesh and container is therefore preferred forfeeding the magnet powder.

The circulating apparatus is preferably located in a chamber filled withinert gas, so as to prevent oxidation of the powder, such as Nd₂ Fe₁₄ Bor Sm--Co powder. The chamber may be in the form of a dome or an annulartunnel covering the rotary die.

A green compact of magnet material may be demagnetized until or after itis withdrawn from a rubber mold. The demagnetization is howeverunnecessary when the magnetization of the green compact is low.

According to a preferable demagnetization method, a green compact isdemagnetized in a rubber mold while the load from a pusher(s) isrelieved but is still applied on the green compact. This demagnetizationmethod drastically lessens the stress due to the magnetization and hencedanger of cracking the green compact.

Wet Die-pressing

The above-described constitutions of the present invention are appliedto the third method, i.e., the wet die-pressing with the use of a rubbermold and a slurry of powder and solvent i.e., water or organic solvent.The proportion of the powder to solvent is not limited but is preferablyfrom 2 to 4 weight parts of solvent to from 8 to 6 weight parts ofpowder. A feature employed in the wet-die pressing with the use of arubber mold is that the rubber mold is open at the top, because thewater or the like must be withdrawn from the mold interior through afilter and a suction channel of the upper punch, during the pressingwith the use of the upper punch. Since the rubber mold is open at thetop, the compacting is less isostatic than in conventional pseudo CIP.Note, however, this CIP is a dry type, in which the powder is completelysurrounded by the pressure medium, i.e., the rubber. But a satisfactoryorientation is attained due to the presence of a solvent which reducesthe friction between the powder particles. Furthermore, the pressurefrom the lateral portion of the rubber mold promotes removal of thesolvent and, hence, the draining speed of the solvent is high. Thepressing efficiency is therefore very high.

The slurry may be preliminarily injected into a rubber mold outside adie-press machine and the rubber mold is then loaded in the die-pressmachine; or, the rubber mold may be preliminarily loaded in a die-pressmachine and the slurry may be injected into the rubber mold. Theinjection of slurry into a rubber mold may be carried out by thefollowing methods: preliminarily evacuating the rubber mold to a vacuumand the slurry is then injected; after injecting the slurry into arubber mold, the slurry is exposed to vacuum or reduced pressure; or theslurry is injected into a rubber mold at a high pressure. These methodsprevent blow holes from remaining on the surface of a rubber mold andhence prevent failure of products due to the blow holes. Referring toFIG. 33 an embodiment of the wet die-pressing apparatus according to thepresent invention is illustrated. The wet die-pressing apparatuscomprises: a power source 30 for generating the magnetic field; ahydraulic unit 31; hydraulic cylinders 32, 33; a filter 34 consisting offilter paper or cloth; rolls 35 for winding the filter 34; suctionchannel 36 formed through the upper punch la; a water-suction pump 38; amotor 39 for driving the water-suction pump; and a feeder 42 of thepowder materials. The apparatus also comprises parts other than theabove mentioned; these are denoted by the same reference numerals asshown in FIG. 16.

The suction channel consists of through-holes having a diameter of 1 mmor more so as to enhance the suction efficiency of the pump. The feeder42 is connected with a source of the pressurized air-source (not shown),if it is necessary to feed the slurry with pressure. When the feeder 42completes feeding of slurry into the rubber mold 10, the feeder shuntsoutside the compacting region of the punches 1a, 1b. The hydraulic unit31 feeds the pressure medium into the hydraulic cylinder 32 and forcesthe upper punch la and the filter 34 to move down until the filter 34covers the open top of the filter 34 to move down until the filter 34covers the open top of the rubber mold 10. The lower punch 1b is thenpushed upwards. Simultaneously, the suction pump 38 is operated to suckthe water through the suction channel 36. When the suction of water iscompleted, the lower punch 1b is further pushed upwards. When the spacebetween the upper punch 1a and the die 2 is closed, the power source 30energizes the electromagnetic coils 4, which generates then the magneticflux permeating through the upper and lower punches 1a, 1b. Thecompacting of powder by the upper and lower punches 1a, 1b is thencarried out. Upon completion of the die-pressing, the steps, which arein reverse sequence to those described above, are carried out. The rolls35 are rotated to reel the filter 34 and to expose an unused section ofthe filter 34.

FIG. 34 illustrates the essential part of another embodiment of thewet-type die-pressing apparatus according to the present invention. Thisapparatus is the same as illustrated in FIG. 33, except that the filter34 is a ceramic filter. The continuous pores in the ceramic, whichcommunicate its inner and outer surfaces with one another, are utilizedas water-sucking channels. After die-pressing, high-pressure air isblown through the pores to remove the powder remaining there and henceto prevent clogging. The ceramic filter 34 is therefore used a number oftimes. A plaster filter, which is very inexpensive and is easilyavailable, can be used as the ceramic filter 34. A filter which has atwo-layer structure for enhancing the durability and water-suctionproperty can also be used as the ceramic filter 34.

Referring to FIG. 35, operation of the apparatus with the use of aceramic filter is illustrated.

First, the upper punch is lowered from the upper limit to the lowerlimit, and then stops. At virtually the same time as the descendingmovement of the upper punch stops, the power source is switched on.Immediately thereafter, the suction pump is energized, that is, apositive magnetic field is applied with the aid of the power source tothe powder to orient it, while the water is removed by the suction pumpfrom the slurry during the orientation. Simultaneously with theenergization of the vacuum pump, the lower punch is pushed upwards toremove water from the slurry. The lower punch is further pushed upwardsuntil the upper limit so as to compact the powder to the desireddensity. The power source is then switched off and is then againswitched on to generate a negative magnetic field which is weaker thanthe positive magnetic field. This negative magnetic field reduces theremaining magnetization of a green compact to facilitate its subsequenthandling. During the operations as described above, the suction pump iskept energized to further remove the water. The suction pump, powersource and lower punch are all de-energized. After this, the upper punchis pushed upwards and the pressurized gas is blown through the filter toremove the clogging. The above series of operations is controlled by amicrocomputer or sequence apparatus. For example, 20 seconds isnecessary for one cycle consisting of the above steps, while in theconventional wet die-pressing approximately 90 seconds are necessary forone cycle. In the present invention, the period of one cycle is shorterthan in the conventional method, because the water removeal speed ishigh and the friction between the powder and die is excluded.

A noticeable phenomenon, discovered in the wet-die pressing with the useof a rubber mold, is that a green compact may crack when the powder isfilled to a point lower than the upper surface of a rubber mold. Anothernoticeable phenomenon is that, when the upper surface of powder filledin a rubber mold, particularly in one having a concave configuration ofthe upper surface, rises higher than the upper surface of the rubbermold, the rising portion of powder is pushed out of the die cavity ontothe upper surface of the rubber mold, thereby forming a burr. In orderto decrease incidence of these phenomena described above, the slurry ispreferably injected into a rubber mold such that the profile of itsupper surface is coincident with the profile of the lower surface of theupper punch. Preferred methods for such injection are: increasing thewater content of the slurry to as high as 60% by weight or more; andusing a guide-plate 105 shown in FIG. 36. The slurry is injected throughthe inlet 107 into the rubber mold 10. Subsequently, the guide-plate 105is moved in the direction of the arrow to rub off the slurry, or islifted up.

Another phenomenon discovered is that the slurry and air in the cavityof the rubber mold are liable to form bubbles on the wall surface of therubber mold, and, further, surface defects such as indentations and thelike are formed on the green compact. A preferred method for decreasingthe incidence of such phenomena is to add into the slurry such defoamingagents as methyl alcohol and ethyl alcohol. Another preferred method isto treat, before or after filling a rubber mold with slurry, the insideof a rubber-mold cavity with reduced pressure. A rubber mold may beplaced in a gas-tight chamber and exposed to vacuum in this chamber.

FIG. 37, illustrates an apparatus for injecting the slurry, adjustingthe upper profile of the slurry, and treating the rubber mold withreduced pressure.

A rubber mold 10 is fixed to the pedestal 130 and side-holder 131. Avacuum-container 132 made of acryl resin is fixed gas-tightly to theside-holder 131 via the packing 133. A piston 135 is gas-tightly andreciprocatively mounted in the central top aperture of the container 132via the packing 134. A collar 137 is secured to the piston 135 at aplace outside the vacuum-container 132. A spring 136 is fitted betweenthe collar 137 and the top of vacuum-container 132 to normally bias thepiston 135 upwards. A stopper 142 is attached to the front end of thepiston 135, and a conduit 138 for feeding the slurry is secured in thestopper 142. The conduit 138 is gas-tightly attached to thevacuum-container 132 via the packing 139 and is displaced in andretracted from the vacuum-container 132. The conduit 138 therefore movesvertically along with the vertical movement of the piston 135. Adetachable plate 140, which is secured to the stopper 142, isstrengthened by a partition plate 141, which consists of material, suchas fluorine plastic whose water-wettability is small. The strengthenedplate 140 has in the central top part a passage which can be closed bythe electromagnetic valve 149. The lower surface of the partition plate141 has the same shape as the lower surface of the upper punch.

The apparatus shown in FIG. 37 is operated as follows.

The electromagnetic valve 149 is closed. The partition plate 141 isattracted by the piston 135 and both are lifted into a position shown bythe dotted lines. The opening 145 for introducing air is closed, and thevacuum container 132 is evacuated through the opening 144. The piston135 is then pushed downwards so as to press the strengthened plate 140against the rubber mold 10 and hence to bring the plate 140 into contactwith the rubber mold 10. The electromagnetic valve 141 is then opened byremote control outside the vacuum container 132. The slurry is then fedthrough the conduit 138 into the rubber mold 10 with the aid ofhigh-pressure gas. Air is then introduced into the vacuum container 132through the opening 145. The piston 135 is then lifted above to lift thevacuum container 132 by hanging it on the stopper 142.

The slurry may, however, not only be injected as illustrated in FIGS. 33and 37 but may be preliminarily compacted and then filled in a rubbermold 10 as illustrated in FIG. 38.

A piston 151 slides on the walls 152, 153 of a slurry-extruder 160,compresses the slurry 15 and extrudes it through the outlet of theslurry-extruder 160 as the pre-compact 15a. The pre-compact 15a isextruded onto the retractable bottom 159 and is then cut by lowering acutter 158. After cutting, the pusher 157 is lowered by sliding it onthe cutter 158 and the wall 161. The pusher 157 is stopped when itsbottom surface strikes the upper surface of the pre-compact 15a. Theretractable bottom 159 is then retracted, and the pre-compact is pushedinto the rubber mold 10s, 10k by means of the pusher 157.

FIG. 39 illustrates a circulating type apparatus for wet-die pressing.The same parts as those shown in FIGS. 22 and 28 are denoted by the samereference numerals. A slurry-filling device shown in FIG. 28 or aloading device of a pre-compact shown in FIG. 29 is installed atposition A. The filling of slurry and vacuum-suction are carried out atposition A by the source of high-pressure air 166. Alternatively, onlythe filling of slurry is carried out at position A and the vacuumsuction is carried out at position B by the vacuum-pump 165. Vacuumchambers 132 may be installed at positions A and/or B to locate therubber molds therein.

Rubber Molds

A rubber mold according to the present invention for forming a hollowgreen compact comprises a mandrel which is harder than the otherportions of the rubber mold. If the mandrel of the rubber mold is softerthan the other portions of the rubber mold, the mandrel 10m (FIG. 40)shrinks in the radially inner direction when pressure is applied by thepunch(es) to the rubber mold. When the punch(es) is later retracted, theload applied to the rubber mold 10 and powder is relieved, with theresult that the mandrel 10m, which has been shrunk once, pushes thegreen compact and expands to enlarge the hole of a green compact 5. Thegreen compact 5 may therefore crack. The rubber mold according to thepresent invention lessens the shrinkage of the mandrel 10m and henceprevents the cracking of a green compact. The hollow green compact canbe either radially or axially oriented.

A rubber mold for forming a hollow green compact may be provided withtwo mandrels 10m, 10m'. The upper punch 1 is provided with a recess 1a'for guiding the mandrel 10m. The mandrels 10m, 10m' may consist ofmetal.

Preferable structures of the rubber mold used for both dry and wetdie-pressing methods according to the present invention are nowdescribed. In this description the upper, lower and side portions of arubber mold are referred to as the top, bottom and side wall,respectively. In addition, at least the surface part of the aboveportions in contact with the powder should consist of materials, or havehardness, as described hereinafter.

According to one of the preferable rubber molds, at least either the topor bottom is harder than the wall part. If, on the contrary, the wallpart is harder than the top and/or bottom, such incidence as isschematically shown in FIG. 42 occurs. That is, the deformation of theside wall 10s causes a considerable shrinkage of the (soft) bottom 10kto form wrinkles on it. These wrinkles act as the starting points ofcracks 5'. In addition, the soft bottom 10k is liable to seize thepowder, and the friction between the bottom 10k and the powder is great.When the pressure of a punch(es) is relieved, the bottom 10k tends to berestored to its original shape and hence to deform in the reversedirection from that during the compacting. At the reverse deformation,since the seizure between the bottom 10k and the green compact hasoccurred during the compacting, the green compact 5' follows thedeformation of bottom 10k. The green compact 5' may therefore crack.

When the bottom 10k is of the same hardness as the side wall 10s, thenthe cracks are formed as described with reference to FIG. 42, when thedegree of deformation is high. The preferable rubber mold thereforeconsists of a hard bottom and/or top made of metal or hard rubber orresin.

According to another preferable rubber mold, at least either the top orbottom has a thickness (t, unit-mm) defined by t≦16 h/D (h is thicknessof a green compact in mm, and D is the positive root of cross-sectionalarea (mm²) of the green compact). The thickness of a bottom and thethickness of a green compact mean those in the pressing direction by apunch(es). The cross-sectional area of a green compact is the area ofthe cross section in the direction perpendicular to the pressingdirection by a punch(es). As the area of a green compact becomes greater(smaller value for the right side of the formula above), the inversedeformation force of a rubber mold becomes greater, thereby causing thegreen compact to crack easily. The thickness of the top and/or bottom istherefore decreased. The effect of the thickness (h) to prevent cracksis illustrated in FIG. 42. The bottom 10k is compressed by the upperpunch 1a generating the pressure Pa (FIG. 43) and the lower punch 1bgenerating the pressure Pd in the other direction. The pressure Pc isthe shrinking stress reducing the cross-sectional area or the side wall10s and the green compact. The wrinkles are generated by the pressurePc. The thinner the bottom 10k, the greater is the pressure Pa and Pb,thereby holding stronger the bottom 10k. When the holding force exceedsthe pressure Pc, wrinkles do not generate.

The coefficient "16" of the above formula was obtained from thefollowing experiments. That is, the coefficient "16" was confirmed to becritical for the incidence of cracks of green compacts formed with theuse of rubber molds shown in FIGS. 36(E) and (F) and having dimensionsof 30×30×5 mm and h/D=0.17. Powders of Nd--Fe--B and Fe--Co magnets werecompacted under the pressure of 1.0 ton/cm².

The above-described two preferable rubber molds can be embodied asexamples shown in FIG. 44. In this drawing, the hatched part consists ofmetal or hard rubber. The thickness of the top and/or bottom satisfyingthe above equation is referred to as "thin".

In FIG. 44(A), the top 10u, side wall 10s and bottom 10k consist of softrubber, soft and hard rubber, or metal.

In FIG. 44(B), the top 10u, side wall 10s and bottom 10k consist of softrubber, soft and hard rubber, or metal.

In FIG. 44(C), the thin top 10u, side wall 10s and bottom 10k consist ofsoft rubber, soft and hard rubber, or metal.

In FIG. 44(D), the thin top 10u, and the integral side wall 10s andbottom 10k consist of soft rubber.

In FIG. 44(E), the top 10u, and the integral side wall 10s and bottom10k consist of hard rubber or metal and soft rubber, respectively.

In FIG. 44(F), the top 10u, and the integral side wall 10s and thinbottom 10k consist of soft rubber.

In FIG. 44(G), the top 10u consists of hard rubber or metal, and theintegral side wall 10s and thin bottom 10k consist of soft rubber.

In FIG. 44(H), the thin top 10u, and the integral side wall 10s and thinbottom 10k consist of soft rubber.

In FIG. 44(I), the top 10u, side wall 10s and bottom 10k consist of hardrubber or metal, soft and hard rubber, or metal.

In FIG. 44(J), the side wall 10s and bottom 10k consist of soft and hardrubber or metal, respectively, and the bottom 10k is rigidly inserted inthe recess formed in the side wall 10s.

In FIG. 44(K), the side wall 10s and bottom 10k consist of soft and hardrubber or metal, respectively, and the bottom 10k is rigidly inserted inthe recess formed in the inner side surface of the side wall 10s.

In FIG. 44(L), the top 10u is provided with a projection protrudingdownwards and consists of hard rubber or metal. The side wall 10s andthe bottom 10k consist of soft and hard rubber or metal, respectively.

The top 10u consisting of metal as shown for the example in FIG. 44(E)can be embodied in the upper punch of a die-press machine. In addition,the bottom 10k consisting of hard metal can be embodied in the lowerpunch of a die-press machine.

The above described relationship of hardness and thickness of theportions of a rubber mold are not preferable for an elongated greencompact, because the phenomena occurring during the compacting are justopposite to the one described above. The elongated compact is one havinga length two times greater than the width thereof. The flat compact isone having a width two times greater than the length thereof. The widthis defined as the positive square root of the cross-sectional area of agreen compact. In the compacting of a flat green compact, thecompression from the wide opposite ends, where the area is greater thanthe side surface, is decisive for preventing the cracks. Contrary tothis, in the compacting of an elongated green compact, the compressionof powder from the side surface is decisive for preventing the cracks,specifically the laminar cracks shown in FIG. 58. It is thereforepreferred to construct a rubber mold for a flat green compact such thateither top or bottom or both of a rubber mold, which face(s) thepunch(es) of a die-press machine be harder than the side portion of therubber mold. It is therefore preferred to construct a rubber mold for anelongated green compact so that the side portion of a rubber mold isharder than either top or bottom or both of a rubber mold.

Preferably, a rubber mold has a dual-layer structure, such that aportion of a rubber mold in contact with the fine powder consists ofhard material and the other portion, distant from the die cavity,consists of soft rubber. In this dual-layer structure, the fine powderis not seized by the hard rubber, thereby facilitating withdrawal of thegreen compact from the rubber mold.

The harder rubber herein indicates that is harder than the softer rubberby at least 10% in terms of hardness A stipulated in JIS. However, whenthe so determined hardness is greater than 100, the above relationshipis not observed but the harder rubber has a hardness A of 100.

The dual-layer rubber mold can be produced by molding or injectionmolding the hard and soft materials. The side, top and/or bottom portioncan have the dual-layer structure. The dual-layer structure can beprovided by applying hard material on the inner surface of a rubbermold, which has been preliminarily produced. The dual-layer structuremay be such that the portion of a rubber mold in contact with the finepowder has a low coefficient of friction. Lubricant, such as molybdenumdisulfide and the like, may be incorporated in the rubber or resin.Alternatively, polyethylene tetrafluoride (PTFE) and other resin havinga low coefficient of friction may be used as the inner layer of therubber mold.

In the production apparatuses of a magnet described above, the rubbermold 10 and the die 2, which is detachably mounted in the circuit, maybe circulated together.

In an embodiment where the rubber molds are circulated by rotationthrough the positions where such members (42, 4a, 60, 65, 132) of theapparatus for treating the magnet powder are arranged, a motor must beintermittently activated and stopped accurately at the positions,particularly the die-pressing position. At this position, the punch andthe die must be aligned very accurately, so that the requirementaccuracy in the stopping position of the rubber mold can be verystrictly observed.

According to a preferred embodiment which eases such strict requirementsfor accuracy in activating/stopping the motor, the circuit has theconfiguration of an equiangular polygon, equilateral polygon or scalenepolygon, and said members are located at the apex region and/or sideregion of said equilateral or scalene polygon. There is also provided ameans for transporting the rubber mold in a linear movement between theadjacent apexes. The linear movement can be easily attained by means ofa hydraulic cylinder or the like. A particular advantage of the scalenepolygonal configuration is that the distance between the adjacentapexes, where the successive two treatments are carried out, can beappropriately determined taking into consideration the size of saidmembers, treatment time at each step and the like. One or moretreatments may be carried out at each apex.

According to a preferred embodiment of the polygonal circuit, it is ofquadrilateral configuration. In this case, a means for transporting arubber mold may comprise rails extending between the adjacent apexes andat least two palettes slidably mounted on the rails and supporting therubber mold and the die. In this embodiment, said members are arrangedin such a manner that by the circulating movement of the transportingmeans the magnet powder is transferred to the successive treatingpositions.

FIGS. 46 through 51 show preferred embodiments of the productionapparatus for making magnets.

The palette 201 (FIG. 46) is a quadrilateral plate for carrying therubber mold 10 and the die 2. The palette 201 is carried on the rail 241via the ball bearings 242. The palette 201 is provided with downwardprojections 243, in which the ball bearings 242 are rotatably mounted.Instead of the ball bearings, a wheel 241 (FIG. 47) may be guided alongthe rail 248. The wheels 248 may be secured at the four corners of thepalette 201.

The palette 201 (FIG. 47) comprises a movable stage 202 insertedvertically slidably therein and supporting the die 2 on its top surface.The movable stage 202 is resiliently mounted on the body of the palette201. For this resilient mounting, the springs 245 are inserted betweenthe horizontally protruding portion of the movable stage 202 and theL-shaped section rigidly secured to the bottom of the palette 201.

The feeder of powder, the removing device, the magnetic-field generator,the precompacting device, and the die-press machine are linearlyarranged on the straight passage at positions A, B, C, D, and E (FIG.48). A pallete (not shown) therefore moves from A position via C, D andE to B position and stops at the respective positions for the respectivetreatment. The order of arrangement of the feeder and the like is notrestricted.

The upper punch 1a (FIG. 46) lowers to be brought into contact with themovable stage 202, while compressing the springs 245. When the movablestage 202 further lowers, it pushes the metal plate 240. The compactingof the powder then starts. The resilient mounting as is shown in FIG. 46therefore mitigates the force of the upper punch la and hence preventstrouble from occurring due to excessive load during the die pressing.

The operation of the apparatus shown in FIG. 49 is now described.

The guide plate 214 covers the palette 202. The arm 206 is secured tothe guide plate 214, and the pneumatic piston 208 is secured on the arm206 via a vertical column 207. The pneumatic cylinder 208 is providedwith horizontally movable piston rod 208' and actuates the piston rod208'. A hopper of powder 209 is secured on the piston rod 208' and ishence horizontally displaced relative to the palette 202. The pneumaticcylinder 210 actuates the pusher 211 and is horizontally displaced bythe pneumatic cylinder 208. The four palettes 201 are carried by theframe 232.

The driving means of the arm 206 is denoted by the reference numeral230.

When the palette 202 is positioned directly below the guide plate 214,the arm is driven downwards to press the guide plate 204 against therubber mold. Then, the powder is fed from the hopper 209 via the feeder205 which is tightly attached to the guide plate 204, into the rubbermold. The pneumatic cylinder 208 is then actuated to retract the hopper209 and simultaneously advance the pusher onto the position directlyabove the guide plate 204. The pneumatic cylinder 210 is then actuatedto lower the pusher 211, which then slides along the side wall of theguide plate 204 and presses the powder into the rubber mold. The pusher211 is then elevated. The arm 206 is elevated to retract the hopper 209and guide plate 204 upwards. The palette 202 is then transferred fromthe position A to the position B.

In position B, the pulse coil 215 is carried on the frame which is heldby the vertical columns 213. The pulse coil 215 is lowered by ahydraulic cylinder 214 to cover the die. The cover 216 is simultaneouslylowered to shield the die so as to prevent the powder from scatteringoutside the die during the magnetization. After the magnetization, thepulse coil 215 is lifted. The palette 202 is then transferred fromposition B to position C.

At position C, the die-press machine comprising the upper punch 219 andthe hydraulic cylinder 217 is located. These members are carried by aframe which is held by the vertical columns 218. The pressing as isillustrated with reference to FIG. 46 is carried out at position C.

The palette 202 is transferred from position C to position D, where thegreen compact 228 is taken out of the rubber mold by the method as isdescribed with reference to FIG. 31. A magnetic pole in the form of apin 223 is lowered by the pneumatic cylinder 222 to magnetically attractthe green compact 228 which has been compacted in the rubber mold 231.The pneumatic cylinder 222 is secured on the arm 224 which is swivelledaround the shaft 225 by motor 226. The green compacts 228 are conveyedby the conveyor 227.

FIGS. 50 and 51 illustrate a means for transferring the palette 201. Amotor 260 for driving the transferring of the palette 201 is secured tothe upper frame 270. The upper frame 270 is supported by the lower frame268. The gear 267 is driven directly by the motor 260, and a chain 268is wound around the gear 267 and the other gear 261 which is secured tothe upper frame 270. The chain 268 is provided with clicks 255.

The palettes 201 are also provided with clicks 252 at the four cornersat such a position that they 252 can be engaged with the clicks 255 onthe chain 268. The palettes 201 are carried via the wheels on the rails251, which are extended along each side of the upper frame 270.

The palettes 201 can therefore be transferred between, for example,positions A and B. When the click 255 is displaced to an extremeposition, for example position B in FIG. 50, it pushes the palette 201so that an appropriate clearance is formed therebetween 201 and 255,thereby making it possible to move the click 255 along the gear 267toward the lower side of the chain 268. The click 255 further moves andstops at position A. The click 255 stops there until the time of thenext transfer.

The present invention is hereinafter described by way of Examples.

EXAMPLE 1

(Nd--Fe--B Sintered Magnet)

The rubber mold shown in FIG. 45 was used. The cover 10u was made ofmetal. The side wall 10s and the bottom 10k were made of integral softurethane rubber (hardness 40 in JIS A). The back-up plate 12 made ofhard urethane rubber (hardness 90) was located under the bottom 10k, soas to prevent the rubber of the bottom from being seized in theclearance between the die and the punch(es). The dimension of moldcavity was 30 mm, 30 mm and 5 mm.

Metallic neodymium (Nd), electrolytic iron (Fe), metallic boron (B) andmetallic dysprosium (Dy) were blended to provide a composition of Nd₁₃.8Dy₀.4 Fe₇₈.2 B₇.6 and were then arc-melted in argon gas to provide aningot. The ingot was then roughly crushed by a stamp mill to provide anaverage particle-diameter of 20 μm and, then finely milled by a jet millto provide an average-particle diameter of 3.0 μm. The so-provided finepowder was filled in the rubber mold 10s, 10k by means of vibration andpressure by a pusher, so that a filling density of from 1.0 to 4.2 g/cm³(13-56%) was attained. The rubber mold 10s, 10k was covered with theupper cap 10u, and then pulse magnetic field of 40 kOe was applied fivetimes, each for 5μ seconds. Subsequently, the rubber mold was located ina die-press machine. The axial pressing was carried out under pressureof 0.8 ton/cm² and magnetic field of 12 kOe. The obtained green compactswere sintered at 1100° C. for 2 hours. The sintered compacts were agedat 650° C. for 1 hour. The magnetic properties of the sintered compactsand the quality of the green compacts are given in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Filling Density                                                                       1.0                                                                              1.4 1.8                                                                              2.2 2.6                                                                              3.0 3.4                                                                              3.8 4.2                                       (g/cc)                                                                        Cracks and                                                                            C  B   A  A   A  A   A  A   A                                         Crazings                                                                      Deformation                                                                           C  B   B  B   A  A   A  A   A                                         Br(kG)  12.5                                                                             12.5                                                                              12.5                                                                             12.5                                                                              12.5                                                                             12.5                                                                              12.3                                                                             12.0                                                                              9.4                                       (BH).sub.max                                                                          37.2                                                                             37.2                                                                              37.2                                                                             37.2                                                                              37.2                                                                             37.2                                                                              36.0                                                                             34.3                                                                              21.0                                      iHc(k0e)                                                                              14.2                                                                             14.2                                                                              14.2                                                                             14.2                                                                              14.2                                                                             14.2                                                                              14.4                                                                             14.6                                                                              14.7                                      __________________________________________________________________________

The filling density of 1.0 g/cc corresponds to the comparative example,in which the filling was natural filling.

The criteria of the cracks and fracture were as follows.

A: Neither cracks nor fracture

B: Cracks and fracture less than 10% of the total number of the greencompacts

C: Cracks and fracture 10% or more of the total number of the greencompacts

The criteria of deformation of green compacts were as follows:

A: Virtually no non-uniform deformation. Slight non-uniformity mayremain in a green compact. In this case, a virtually complete greencompact can be obtained by modifying the inner shape of the rubber mold.

B: Some non-uniform deformation but to such an extent that can becorrected by subsequent machining.

C: Non-uniform deformation is so serious that it is impossible to adjustthe dimension of the green compacts by subsequent machining. Improvementis difficult even by improving the rubber mold.

The above criteria are used also for the subsequent examples unlessotherwise mentioned.

EXAMPLE 2

(Sintered Sm--Co magnet)

The rubber mold used in Example 1 was used. The ingot used had acomposition of Sm(Co₀.72 Fe₀.2 Cu₀.06 Zr₀.03)₇.3. This ingot was roughlycrushed by a stamp mill to provide an average particle-diameter of 25 μmand then finely milled by a jet mill to provide an average-particlediameter of 3.5 μm. The so-provided fine powder was filled in the rubbermold 10s, 10k by means of vibration and pressure by a pusher, so that afilling density of from 1.1 to 4.9 g/cm³ (13-58%) was attained. Therubber mold 10s, 10k was covered with the cover 10u, and thenpulse-magnetic field of 40 kOe was applied five times, each for 5μseconds.

Subsequently, the rubber mold was placed in a die-press machine. Theaxial pressing was carried out under pressure of 0.8 ton/cm² andmagnetic field of 12 kOe. The obtained green compacts were sintered at1215° C. for 1 hour. The sintered compacts were aged at 805° C. for 2hours and then cooled gradually.

The magnetic properties of the sintered compacts and the quality of thegreen compacts are given in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Filling Density                                                                       1.1                                                                              1.6 2.1                                                                              2.6 3.1                                                                              3.6 4.1                                                                              4.6 4.9                                       (g/cc)                                                                        Cracks and                                                                            C  B   A  A   A  A   A  A   A                                         Crazings                                                                      Deformation                                                                           C  B   B  A   A  A   A  A   A                                         Br(kG)  11.2                                                                             11.2                                                                              11.2                                                                             11.2                                                                              11.2                                                                             11.1                                                                              10.9                                                                             10.0                                                                              8.4                                       (BH).sub.max                                                                          30.9                                                                             30.9                                                                              30.9                                                                             30.9                                                                              30.9                                                                             30.3                                                                              29.3                                                                             24.6                                                                              17.4                                      iHc(k0e)                                                                              17.2                                                                             17.2                                                                              17.2                                                                             17.2                                                                              17.2                                                                             17.3                                                                              17.5                                                                             17.6                                                                              17.6                                      __________________________________________________________________________

The filling density of 1.1 g/cc corresponds to the comparative example,in which the filling was natural filling.

EXAMPLE 3

(Sintered Ferrite Magnet)

The rubber mold used in Example 1 was used. The raw materials used werecommercial strontium carbonate (SrCO₃) and commercial ferric oxide (Fe₂O₃). The respective raw materials were blended in a molar proportion of1:5.9 and were then crushed and mixed for 5 hours. The mixture wascalcined at 1270° C. for 1 hour. The calcined sample was roughly crushedby a stamp mill to provide an average particle diameter of 4 μm andsubsequently finely milled by a ball mill to provide an averageparticle-diameter of 0.7 μm. The finely milled powder was dried in air,and subjected to dry pressing. The so-provided fine powder was filled inthe rubber mold 10s, 10k by means of vibration and pressure by a pusher,so that a filling density of from 0.6 to 2.8 g/cm³ (13-58%) wasattained. The rubber mold 10s, 10k was covered with the cover 10u andthe magnetic field of 40 kOe was applied five times each for 5 useconds. Subsequently, the rubber mold was placed in a die-pressmachine. Axial pressing was carried out under pressure of 0.8 ton/cm²and magnetic field press-forming was carried out under pressure of 0.8ton/cm² and magnetic field of 12 kOe. The obtained green compacts weresintered at 1200° C.

The magnetic properties of the sintered compacts and the quality of thegreen compacts are given in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Filling Density                                                                       0.6                                                                              0.8 1.0                                                                              1.2 1.4                                                                              1.6 1.8                                                                              2.0 2.2                                       (g/cc)                                                                        Cracks and                                                                            C  B   A  A   A  A   A  A   A                                         Crazings                                                                      Deformation                                                                           C  B   B  A   A  A   A  A   A                                         Br(kG)  3.80                                                                             3.93                                                                              4.02                                                                             4.02                                                                              4.02                                                                             3.92                                                                              3.82                                                                             3.61                                                                              3.02                                      (BH).sub.max                                                                          3.44                                                                             3.63                                                                              3.80                                                                             3.80                                                                              3.80                                                                             3.60                                                                              3.43                                                                             3.06                                                                              2.14                                      iHc(k0e)                                                                              2.8                                                                              2.8 2.8                                                                              2.8 2.8                                                                              2.8 2.9                                                                              2.9 3.0                                       __________________________________________________________________________

The filling density of 0.6 g/cc corresponds to the comparative example,in which the filling was natural filling.

EXAMPLE 4

The raw-material powder used was the one prepared for a resin-bondedmagnet and had a composition of Sm(Co₀.72 Fe₀.2 Cu₀.06 Zr₀.03)₇.3, 20 μmof average particle-diameter and coercive force (iHc) of 15.5 kOe. Thispowder together with epoxy-resin powder was filled in the rubber mold10s, 10k (c.f. FIG. 36) by means of vibration and pressure by a pusher,so that filling density of from 1.4 to 5.5 g/cm³ (18-65%) was attained.The rubber mold 10s, 10k was covered with the cover 10u, and then pulsemagnetic field of 40 kOe was applied five times, each for 5μ seconds.

Subsequently, the rubber mold was placed in a die-press machine. Theaxial pressing was carried out under pressure of 1 ton/cm² and magneticfield of 12 kOe. The obtained green compacts were cured at 120° C. for 1hour.

The magnetic properties and the quality of the green compacts are givenin Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Filling Density                                                                       1.5                                                                              2.0 2.5                                                                              3.0 3.5                                                                              4.0 4.5                                                                              5.0 5.5                                       (g/cc)                                                                        Cracks and                                                                            C  B   A  A   A  A   A  A   A                                         Crazings                                                                      Deformation                                                                           C  B   B  B   A  A   A  A   A                                         Br(kG)  7.40                                                                             7.40                                                                              7.40                                                                             7.40                                                                              7.40                                                                             7.20                                                                              7.00                                                                             6.50                                                                              5.55                                      (BH).sub.max                                                                          13.5                                                                             13.5                                                                              13.5                                                                             13.5                                                                              13.5                                                                             12.8                                                                              12.0                                                                             10.4                                                                              7.59                                      iHc(k0e)                                                                              15.4                                                                             15.4                                                                              15.4                                                                             15.4                                                                              15.4                                                                             15.5                                                                              15.6                                                                             15.7                                                                              15.7                                      __________________________________________________________________________

The filling density of 1.5 g/cc corresponds to the comparative example,in which the filling was natural filling.

EXAMPLE 5

The raw-material powder used was the ferrite powder prepared for aresin-bonded magnet and had 1.35 μm of average particle-diameter andcoercive force (iHc) of 2.7 kOe. After disintegrating the aggregates ofpowder, 0.5% by weight of epoxy resin was added to the ferrite powder.The ferrite powder together with epoxy-resin powder was subjected to thesame process as in Example 4, except that the die-pressure was 0.8ton/cm² and curing time was 2 hours.

The magnetic properties and the quality of the green compacts are givenin Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Filling Density                                                                       0.6                                                                              0.8 1.0                                                                              1.2 1.4                                                                              1.6 1.8                                                                              2.0 2.2                                       (g/cc)                                                                        Cracks and                                                                            C  B   A  A   A  A   A  A   A                                         Crazings                                                                      Deformation                                                                           C  B   B  A   A  A   A  A   A                                         Br(kG)  2.20                                                                             2.26                                                                              2.33                                                                             2.33                                                                              2.33                                                                             2.26                                                                              2.19                                                                             1.98                                                                              1.75                                      (BH).sub.max                                                                          1.13                                                                             1.19                                                                              1.27                                                                             1.27                                                                              1.27                                                                             1.19                                                                              1.13                                                                             0.92                                                                              0.72                                      iHc(k0e)                                                                              2.69                                                                             2.69                                                                              2.69                                                                             2.69                                                                              2.69                                                                             2.69                                                                              2.70                                                                             2.71                                                                              2.71                                      __________________________________________________________________________

The filling density of 0.6 g/cc corresponds to the comparative example,in which the filling was natural filling.

EXAMPLE 6

(Comparative Example)

The process of Examples 1 through 5 was repeated except for thefollowing items: the powders were filled in a conventional die of thepress machine (without a rubber mold); the filling density of thepowders was adjusted as given in Table 6; and the pressure of axialdie-pressing was 1.5 ton/cm². The results are given in Table 6, as"Axial Die Pressing", while the results of Examples 1 through 5 aregiven in Table 6 as "GDP".

Since the composition and production process of the magnet powders inExamples 1 through 5 are the same as those of the comparative example,the 4 π Is of the magnet powders of the comparative example is the sameas that of Examples 1 through 5. The Br of Examples 1 through 5 ishigher than that of the comparative example by approximately 7%. Thisclearly indicates that the orientation of various magnets can beenhanced by the inventive method more than by axial die pressing. Withregard to iHc, there is approximately a 1% difference between theinventive method and the axial die-pressing, which difference is notappreciable because iHc is very likely to scatter.

                  TABLE 6                                                         ______________________________________                                                                        Filling                                       Pressing   Magnetic Properties  Density                                       Material                                                                             Method  Br(kG)  (BH).sub.max (MG0e)                                                                     iHc(K0e)                                                                             g/cc %                                ______________________________________                                        Nd-Fe-B                                                                              Axial   11.5    31.4      14.4   1.0  13                               Sintered                                                                             GDP     12.5    37.2      14.5   2.2  29                               SmCo   Axial   10.2    24.9      17.8   1.1  13                               Sintered                                                                             GDP     11.2    30.9      17.2   2.6  31                               Ferrite                                                                              Axial   3.82    3.4       2.9    0.6  12                               (Dry,  GDP     4.02    3.8       3.0    1.2  24                               Sintered)                                                                     SmCo   Axial   6.92    11.8      15.6   1.5  18                               (Bond) GDP     7.40    13.5      15.4   3.0  35                               Ferrite                                                                              Axial   2.05    1.0       2.7    0.6  12                               (Bond) GDP     2.33    1.27      2.69   1.2  24                               ______________________________________                                         GDP is the inventive examples with preliminary pulse magnetic field.     

EXAMPLE 7

Metallic neodymium (Nd), electrolytic iron (Fe), metallic boron (B) andmetallic dysprosium (Dy) were blended to provide a composition Nd₁₃.8Dy₀.5 Fe₇₉.5 B₇.0 and were then arc-melted in argon gas to provide aningot.

The ingot was then roughly crushed by a stamp mill in inert-gasatmosphere to provide an average particle-diameter of 20 um. The roughlycrushed powder was then finely milled by a jet mill in nitrogenatmosphere, whose oxygen concentration was less than detectable limit,to provide an average-particle diameter of 3.0 μm. The so-provided finepowder was filled in the rubber mold 10s, 10k by means of vibration andpressure by a pusher, so that filling density of 2.6 g/cm³ (34%) wasattained. The filling of the fine powder was carried out while placingthe rubber mold 10s, 10k in a chamber filled with nitrogen. The fillingof the fine powder in air atmosphere was also carried out, but resultedin ignition of the powder thereby making it impossible to subject thepowder to the subsequent process. Then the filled fine powder wassubjected to the same process as in Example 1, except for aging at 630°C. for 1 hour. The magnetic properties of the sintered compact was:Br=13.9 kOe; (BH)_(max) =45.1 MGOe; and, iHc=12.8 kOe. The oxygenconcentration of the sintered compact was 2680 ppm.

EXAMPLE 8

(Wet ferrite magnet)

Commercial strontium carbonate (SrCO₃) and commercial ferric oxide (Fe₂O₃) were blended in a molar proportion of 1:5.9 and were then milled bya ball mill for 6 hours. The mixture was calcined at 1260° C. for 2hours. After calcining, the sample was roughly crushed and then finelymilled to provide average particle-diameter of 0.75 μm. The obtainedfine powder was rendered to slurry having slurry concentration of 71%(weight percentage of the ferrite powder based on the total weight ofthe slurry).

Arc-shaped green compacts as shown in FIG. 10 were produced using thewet-die press machine shown in FIG. 25 and provided with a filter 34made of cloth or paper, a vacuum suction device and a slurry injectiondevice and also using the wet-die press shown in FIG. 26 and providedwith ceramic filter 34.

The methods employed for slurry injection were of injecting slurry fromupper portion of the rubber mold preliminarily located in a die (FIG.25), or of injecting slurry into the rubber mold outside the pressmachine and then setting the rubber mold in the press machine. Thefilling method employed in the conventional wet method, i.e., injectingof slurry into the die through an aperture formed in the side wall ofthe die, was not employed.

The respective steps of the compression forming were finely adjusted sothat they did not interfere with one another and, further, excess idletime was almost avoided.

The compression forming was repeated one hundred times for each densityand each filling method. For comparison purpose, the conventionalparallel die-pressing (without rubber mold) was carried out one hundredtimes. In order to measure the density and magnetic properties of thesintered magnets, sampling of each sample was carried out for each fivepress cycles and the samples were sintered at 1235° C. for 1.5 hours.The samples for measuring the magnetic properties were cut from thearc-shaped sintered magnets and were subjected to measurement with a BHtracer. The average magnetic properties are given in Table 7.

                                      TABLE 7                                     __________________________________________________________________________          Generation                                                                    of Cracks                                                                           Density                                                                            iHc                                                                              Br  (BH).sub.max                                                                      Filling                                           Filter                                                                              (%)   (g/cm.sup.2)                                                                       (k0e)                                                                            (kG)                                                                              (MG0e)                                                                            Method                                                                             Remarks                                      __________________________________________________________________________    Paper,                                                                              5     4.96 2.8                                                                              4.12                                                                              4.0 within die                                                                         Comparative                                  Cloth                                                                         Ceramics                                                                            4     4.97 2.8                                                                              4.11                                                                              4.0 within die                                                                         Comparative                                  Paper,                                                                              1     4.96 2.8                                                                              4.32                                                                              4.4 outside die                                                                        Inventive                                    Cloth                                                                         Ceramics                                                                            1     4.97 2.8                                                                              4.31                                                                              4.4 outside die                                       Paper,                                                                              1     4.97 2.8                                                                              4.31                                                                              4.4 within die                                        Cloth                                                                         Ceramics                                                                            1     4.96 2.8                                                                              4.32                                                                              4.4 within die                                        __________________________________________________________________________     As is apparent from Table 7, cracks are decreased, and Br and (BH).sub.ma     are n reased according to the present invention.                         

EXAMPLE 9

The slurry used in Example 8 was dried and then the aggregates of powderwere disintegrated for 1 hour in a ball mill, to provide dry powder.Measuring the bulk density of the dry powder revealed to be 0.80 g/cm³.This dry powder was filled in a rubber mold made of silicone rubber,23.95 mm in outer diameter, 12 mm in inner diameter, and 10 mm inheight. The filling methods were the combination of the steps chosenfrom the group as mentioned below. The amount of the powder was soadjusted that it was filled up to the top edge of the rubber mold.Influence of the powder bulk-density in the rubber mold (g/cm³) upon themolding under the magnetic field was investigated.

Filling Methods

(1) The rubber mold is placed on the vibrator, and the filling densityis enhanced by vibration.

(2) The rubber mold is loaded in a tapping machine, and the fillingdensity is enhanced by vibration.

(3) Magnetic field is applied to the powder in a rubber mold to enhancethe filling density due to the attraction force of the magnetic fieldand the attraction force of the magnetized particles of the powder.

(4) Powder granulated under magnetic field is used. The granulatingdegree is such that the particles of the granulated powder easilydisintegrated under the magnetic field.

(5) Relatively strongly granulated and oriented powder was formed undera magnetic field.

(6) Magnetic powder was preliminarily compression-shaped at a pressureof a few tens kg/cm² to enhance the filling density.

Then the powder, whose filling density was enhanced by theabove-mentioned method, was subjected five times to application of pulsemagnetic field of 40 kOe for 5μ seconds for each time. The greencompacts were sintered at 1230° C. for 2 hours. The quality of the greencompacts and the maximum energy product (MGOe) of the sintered compactsare given in Table 8.

                  TABLE 8                                                         ______________________________________                                        Filling   0.8     0.9   1.0   1.1 1.2   1.3 1.4                               Density                                                                       Cracks,   C       B     A     A   A     A   A                                 Crazing                                                                       Deformation                                                                             C       B     B     A   A     A   A                                 (BH).sub.max                                                                            4.4     4.4   4.4   4.4 4.4   4.4 4.4                               ______________________________________                                    

The criterion and cracks was as follows:

A: Virtually neither cracks nor fracture

B: 5% or less of cracks and fracture

C: More than 5% of cracks and fracture

EXAMPLE 10

The fine powder used in Example 1 was compacted by using the dry axialpressing machine whose schematic drawing is shown in FIG. 25. Themagnetic field (H) was oriented to across the mold cavity. A hundredsintered magnets were produced under the same conditions as inExample 1. The magnetic properties of the sintered magnets are given inTable 9.

                  TABLE 9                                                         ______________________________________                                        Magnetic Properties                                                           Br(kG)    (BH).sub.max (MG0e)                                                                       iHc(k0e)     Remarks                                    ______________________________________                                        12.6      38.2        13.5         maximum                                    12.3      36.5        12.8         minimum                                    12.5      37.3        13.1         average                                    ______________________________________                                    

It is possible by means of the method in this Example to continuouslyproduce the magnets with stable properties and to attain automaticproduction of the magnets.

EXAMPLE 11

Commercially available raw material for preparing the ferrite-magnetslurry was used in the conventional axial die-pressing and inventivemethod in Example 3. The green compacts obtained by the respectivemethods were sintered. The magnetic properties of the sintered magnetsare given in Table 10.

                  TABLE 10                                                        ______________________________________                                                   Br          iHc    (BH).sub.max                                    Example    (kG)        (kOe)  (MGOe)                                          ______________________________________                                        Inventive  4.52        2.95   4.86                                            Comparative                                                                              4.30        2.98   4.40                                            ______________________________________                                    

The magnetic properties of this inventive example are better than thoseof Example 3 given in Table 3. The magnetic properties of thiscomparative example are virtually equal to those of the inventiveExample 8. Since ferrite powder having excellent magnetic properties wasused in these inventive and comparative examples, the magneticproperties are excellent even in the comparative example. Since(BH)_(max) of the present inventive example is higher than that of thepresent comparative example by approximately 10%, it is clear thatextremely excellent (BH)_(max) is obtained by using the magnet powderhaving excellent magnetic properties.

EXAMPLE 12

Commercially available raw material of Nd--Fe--B magnet was used in theaxial die-pressing according to Example 1 and the conventional axialdie-pressing. The green compacts obtained by the respective methods weresintered. The magnetic properties of the sintered magnets are given inTable 11.

                  TABLE 11                                                        ______________________________________                                                   Br          iHc    (BH).sub.max                                    Example    (kG)        (kOe)  (MGOe)                                          ______________________________________                                        Inventive  13.2        14.1   40.3                                            Comparative                                                                              12.3        14.3   35.2                                            ______________________________________                                    

Since the Nd--Fe--B powder used in Example 12 has excellent magneticproperties, the magnetic properties of conventional die-pressing areexcellent. (BH)_(max) of the inventive die-pressing is better than thatof the conventional die-pressing by 14%. It is therefore clear thatextremely excellent (BH)_(max) is obtained by using the magnet powderhaving excellent magnetic properties.

EXAMPLE 13

Influence of filling density and application of pulse magnetic fieldupon the magnetic properties were investigated in the process of Example1.

                  TABLE 12                                                        ______________________________________                                        Filling             Magnetic Properties                                       Density   Application                                                                             Br        (BH).sub.max                                                                         iHc                                      (g/cc)    Pulse     (kG)      (MGOe) (kOe)                                    ______________________________________                                        1.4       no        12.5      37.1   14.2                                               yes       12.5      37.2   14.2                                     1.8       no        12.2      35.4   14.3                                               yes       12.5      37.2   14.2                                     2.2       no        11.1      29.3   14.5                                               yes       12.5      37.2   14.2                                     2.6       no        10.1      24.3   14.3                                               yes       12.5      37.2   14.2                                     3.0       no        9.03      19.4   14.4                                               yes       12.5      37.2   14.2                                     ______________________________________                                    

It is clear from Table 12 that the preliminary application of pulsemagnetic field upon the highly densified magnet-powder is effective forenhancing its orientation degree.

EXAMPLE 4

Influence of filling density and application of pulse magnetic fieldupon the magnetic properties were investigated in the process of Example2.

                  TABLE 13                                                        ______________________________________                                        Filling             Magnetic Properties                                       Density   Application                                                                             Br        (BH).sub.max                                                                         iHc                                      (g/cc)    Pulse     (kG)      (MGOe) (kOe)                                    ______________________________________                                        1.6       no        11.2      30.9   17.3                                               yes       11.2      30.9   17.2                                     2.1       no        10.9      29.3   17.3                                               yes       11.2      30.9   17.2                                     2.6       no        9.9       24.1   17.4                                               yes       11.2      30.9   17.2                                     3.1       no        9.0       20.0   17.5                                               yes       11.2      30.9   17.2                                     3.6       no        8.4       17.4   17.5                                               yes       11.1      30.3   17.3                                     ______________________________________                                    

It is clear from Table 13 that the preliminary application of pulsemagnetic field upon the highly densified magnet-powder is effective forenhancing its orientation degree.

EXAMPLE 15

Influence of filling density and application of pulse magnetic fieldupon the magnetic properties were investigated in the process of Example3.

                  TABLE 14                                                        ______________________________________                                        Filling             Magnetic Properties                                       Density   Application                                                                             Br        (BH).sub.max                                                                         iHc                                      (g/cc)    Pulse     (kG)      (MGOe) (kOe)                                    ______________________________________                                        0.8       no        3.89      3.56   2.82                                               yes       3.93      3.63   2.80                                     1.0       no        3.94      3.65   2.81                                               yes       4.02      3.80   2.80                                     1.2       no        3.88      3.53   2.83                                               yes       4.02      3.80   2.80                                     1.4       no        3.26      2.50   2.84                                               yes       4.02      3.80   2.80                                     1.6       no        3.02      2.14   2.84                                               yes       3.92      3.60   2.80                                     ______________________________________                                    

It is clear from Table 14 that the preliminary application of pulsemagnetic field upon the highly densified magnet-powder is effective forenhancing its orientation degree.

EXAMPLE 16

The initial step and the subsequent steps until the fine milling step aswell as the sintering step and subsequent steps were carried outaccording to the same method and under the same conditions as inExamples 1 through 5. The following methods were carried out inComparative Example and Examples A and B.

Comparative Example--axial die-pressing under magnetic field

(compacting pressure--1.5 t/cm², magnetic field 12 kOe)

Example A--A pulsed magnetic field of 40 kOe is applied to highlydensified powder five times, 5μ seconds for each time. The die pressingwas then carried out without the application of magnetic field. Thecompression pressure was 1.0 ton/cm². The compression direction was thesame as application direction of pulse magnetic field.

Example B--A pulsed magnetic was field applied by the same method as inExample B. The axial die-pressing was then carried out without theapplication of magnetic field. The compacting pressure was 1.0 ton/cm².The compression direction was the same as the application direction ofpulse magnetic field.

The magnetic properties of the obtained magnets are given in Table 15.

                  TABLE 15                                                        ______________________________________                                                     Filling                                                                              Magnetic properties                                                          Density  Br    (BH).sub.max                                                                         iHc                                  Material                                                                              Pressing   (g/cm.sup.3)                                                                           (kG)  (MGOe) (kOe)                                ______________________________________                                        Nd-Fe-B Comparative                                                                              1.4      11.7  32.4   14.4                                 Sintered                                                                              Example A  2.6      12.3  36.1   14.3                                         Example B  2.6      12.5  37.2   14.2                                 Sm-Co   Comparative                                                                              1.6      10.5  26.9   17.5                                 Sintered                                                                              Example A  3.1      11.0  29.5   17.3                                         Example B  3.1      11.2  30.9   17.2                                 Ferrite Comparative                                                                              0.8      3.73  3.32   2.9                                  Sintered                                                                              Example A  1.2      3.95  3.67   2.8                                          Example B  1.2      4.02  3.80   2.8                                  Sm-Co   Comparative                                                                              2.0      6.94  11.9   15.6                                 Bonded  Example A  3.5      7.25  12.8   15.5                                         Example B  3.5      7.40  13.5   15.4                                 Ferrite Comparative                                                                              0.8      2.18  1.11   2.7                                  Bonded  Example A  1.2      2.29  1.23   2.7                                          Example B  1.2      2.33  1.27   2.7                                  ______________________________________                                    

EXAMPLE 17

The rubber mold shown in FIG. 44(I) was used. The cover 10u and bottom10k consisted of hard rubber (hardness 90). The side wall 10s consistedof soft rubber (hardness 40). The die cavity of the rubber mold had adimension of 30×30×3 mm.

The rubber mold was produced as follows. The metal die 336 (FIG. 59),whose cavity had the same dimension as that of the rubber mold, wasprepared. A hard urethane plate 334, which had been preliminarily curedand cut, was set on the bottom of the die cavity of the metal die 336. Acore 33 was set on the hard urethane plate 334 at its center. Uncuredrubber (two-pack type urethane rubber curable at normal temperature,product of Dainihon Ink Chemical Co., Ltd.) was defoamed under vacuumand molded on the hard urethane plate 334 to form the side wall 335.

The rubber molds used in the succeeding examples were also produced bythe method as described above.

The fine powder compacted was the atomized powder of Fe--45 wt % Co(average particle diameter of 15 μm and true density of 8.3 g/cc). Thefine powder was compacted under pressure of 1.0 ton/cm². The obtainedgreen compacts were sintered at 1200° C. for 7 hours. Neither lubricantnor binder was added to the fine powder.

The results of compacting and sintering are shown in Table 16.

                  TABLE 16                                                        ______________________________________                                        Filling Density (g/cc)                                                                       2.50   2.80   3.10 3.40 3.70 4.00                              Density relative                                                                             30.1   33.7   37.3 41.0 44.6 48.2                              to True Density (%)                                                           Filling Density/                                                                             1.00   1.12   1.24 1.36 1.48 1.60                              True Density                                                                  Filling Method N      NV     NVP  NVP  NVP  NVP                               Maximum Unit Weight                                                                          6.85   7.57   8.38 9.18 9.99 10.8                              of Green Compacts (g)                                                         Minimum Unit Weight                                                                          6.70   7.56   8.37 9.16 9.98 10.6                              of Green Compacts (g)                                                         Range of Unit Weight                                                                         0.15   0.01   0.01 0.02 0.01 0.02                              Cracks and Crazings                                                                          C      C      B    B    A    A                                 Deformation    C      C      A    A    A    A                                 Density of Sintered                                                                          --     --     94   94   94   94                                Compact/True Density (%)                                                      ______________________________________                                    

(1) The left end column of Table 16 corresponds to the comparativeexample, where the fine powder is filled at the natural density. In thisfilling, the fine powder was fallen under gravity into the rubber mold,and then the rising powder above the rubber mold was rubbed off. Theweight of the fine powder was not measured.

In the inventive examples, the weight of the fine powder filled atvarious densities was measured with a tolerance of ±1%.

(2) The filling methods

N--The natural filling to provide the natural density as described above

NV--The fine powder was dropped into the rubber mold by guiding it witha frame, while imparting vibration to the fine powder. After filling,the upper surface of the filled powder was lightly pushed by a pusher soas to make the upper surface coincident with the upper surface of therubber mold.

NVP--the fine powder was dropped into the rubber mold by guiding it witha frame, while imparting vibration to the fine powder. After filling,the upper surface of the filled powder was strongly pushed by a pusherso as to make the upper surface coincident with the upper surface of therubber mold.

The criteria of the cracks and fracture were as follows.

A: Neither cracks nor fracture

B: Cracks and fracture less than 10% of the total number of the greencompacts

C: Cracks and fracture 10% or more of the total number of the greencompacts

The criteria of deformation of green compacts were as follows.

A: Virtually no non-uniform deformation. Slight non-uniform defromationmay remain in a green compact.

In this case, a virtually complete green compact can be obtained bymodifying the inner shape of the rubber mold.

B: Some non-uniform deformation but to such an extent that can becorrected by subsequent machining.

C: Non-uniform deformation is so serious that it is impossible to adjustthe dimension of the green compacts by subsequent machining. Improvementis difficult even by improving the rubber mold.

The above criteria are used also for the subsequent examples unlessotherwise mentioned.

Ti fine powder (hydrogenated and the decomposed powder, averageparticle-diameter--10 um, and true density--4.5 g/cc) was compacted asin the case of Fe--Co powder at a pressure of 1.0 t/cm². The obtainedgreen compacts were sintered at 115° C. for 6 hours. The results areshown in Table 17.

                  TABLE 17                                                        ______________________________________                                        Filling Density (g/cc)                                                                       0.75   1.00   1.25 1.50 1.75 2.00                              Density relative                                                                             16.6   22.2   27.7 33.3 38.8 44.3                              to True Density (%)                                                           Filling Density/                                                                             1.00   1.34   1.67 2.01 2.34 2.67                              True Density                                                                  Filling Method N      NV     NVP  NVP  NVP  NVP                               Maximum Unit Weight                                                                          0.98   1.20   1.49 1.79 2.09 2.39                              of Green Compacts (g)                                                         Range of Unit Weight                                                                         0.80   1.21   1.48 1.78 2.08 2.40                              Minimum Unit Weight                                                                          0.18   0.01   0.01 0.01 0.01 0.01                              of Green Compacts (g)                                                         Cracks and Crazings                                                                          C      B      A    A    A    A                                 Deformation    C      B      A    A    A    A                                 Density of Sintered                                                                          --     96     96   96   96   96                                Compact/True Density (%)                                                      ______________________________________                                    

EXAMPLE 18

The rubber mold shown in FIG. 60 was used. The cover 10u consisted ofhard rubber (hardness 90). The side wall 10s with integral bottomconsisted of soft rubber (hardness 40). The dimensions of the die cavityof the rubber mold were 47 mm in inner diameter and 17 mm in height. Thefine powders used, compacting pressure and sintering conditions were asfollows.

(1) Fe--2 wt % Si (average particle diameter--10 μm, the truedensity--7.7 g/cc)

Compacting pressure--1.0 t/cm

Sintering temperature--1200° C.

Sintering time: 6 hours (Table 18)

(2) Fe--0.3 wt % C (water-atomized then reduction by hydrogen. Averageparticle diameter--20 μm, the true density--7.8 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature--200° C.

Sintering time: 6 hours (Table 19)

(3) Fe--0.3 wt % C (water-atomized then reduction by hydrogen. Averageparticle diameter--20 μm, the true density--7.8 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature--1200° C.

Sintering time: 6 hours (Table 20)

(4) Fe--42 wt % Ni (atomized powder, average particle diameter--30 μm,the true density--9.1 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature 1200° C.

Sntering time: 6 hours (Table 21)

(5) Fe--42 wt % Ni (atomized powder, average particle diameter--10 μm,the true density--8.1 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature 1200° C.

Sntering time: 6 hours (Table 22)

(6) Ti (hydrogenated and then decomposed powder, average particlediameter--10 μm, the true density--4.5 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature--1150° C.

Sntering time: 6 hours (Table 23)

(7) Al for sintering (atomized powder, average particle diameter--10 μm,the true density--2.7 g/cc)

Compacting pressure--1.0 t/cm²

Sintering temperature--600° C.

Sntering time: 6 hours (Table 24)

                  TABLE 18                                                        ______________________________________                                        Filling Density                                                                        2.30    2.60    2.90  3.20  3.50  3.80                               (g/cc)                                                                        Density relative                                                                       29.9    33.7    33.7  41.6  45.5  49.4                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.13    1.26  1.39  1.52  1.65                               True Density                                                                  Filling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.641   0.639   0.714 0.785 0.861 0.934                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.483   0.634   0.708 0.780 0.857 0.928                              weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of Unit                                                                          0.158   0.005   0.006 0.005 0.004 0.006                              Weight                                                                        Cracks and                                                                             C       C       B     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      98    98    98    98                                 Sintered                                                                      Compact/                                                                      True Density                                                                  (%)                                                                           ______________________________________                                    

                  TABLE 19                                                        ______________________________________                                        Filling Density                                                                        2.45    2.75    3.05  3.35  3.65  3.95                               (g/cc)                                                                        Density relative                                                                       31.4    35.3    39.1  42.6  46.8  50.6                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.12    1.25  1.37  1.49  1.61                               True Density                                                                  Filling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.637   0.675   0.750 0.822 0.896 0.969                              Weight of                                                                     Green                                                                         Compacts                                                                      (g)                                                                           Minimum Unit                                                                           0.563   0.671   0.745 0.817 0.892 0.963                              Weight of                                                                     Green                                                                         Compacts                                                                      (g)                                                                           Range of 0.074   0.004   0.005 0.005 0.004 0.006                              Unit Weight                                                                   Cracks and                                                                             C       C       C     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      --    92    92    92                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

                  TABLE 20                                                        ______________________________________                                        Filling Density                                                                        2.20    2.50    2.80  3.10  3.40  3.70                               (g/cc)                                                                        Density relative                                                                       28.2    32.1    35.9  39.7  43.6  47.4                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.14    1.27  1.41  1.55  1.68                               True Density                                                                  Filling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.640   0.615   0.689 0.762 0.836 0.910                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.477   0.609   0.684 0.765 0.830 0.903                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of 0.162   0.006   0.005 0.007 0.006 0.007                              Unit Weight                                                                   Cracks and                                                                             C       C       B     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      97    97    97    97                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

                  TABLE 21                                                        ______________________________________                                        Filling Density                                                                        2.60    2.90    3.20  3.50  3.80  4.10                               (g/cc)                                                                        Density relative                                                                       32.1    35.8    39.5  43.2  46.9  50.6                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.12    1.23  1.35  1.46  1.58                               True Density                                                                  Filling Method                                                                         N       NV      NV    NVP   NVP   NVP                                Maximum Unit                                                                           0.674   0.714   0.788 0.860 0.934 1.008                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.600   0.708   0.781 0.854 0.926 1.002                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of Unit                                                                          0.074   0.006   0.007 0.006 0.008 0.006                              Weight                                                                        Cracks and                                                                             C       C       B     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      95    95    95    95                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

                  TABLE 22                                                        ______________________________________                                        Filling Density                                                                        2.35    2.65    2.95  3.25  3.55  3.85                               (g/cc)                                                                        Density relative                                                                       29.0    32.7    36.4  40.1  43.8  47.5                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.13    1.26  1.38  1.51  1.64                               True Density                                                                  Tilling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.646   0.652   0.726 0.799 0.874 0.947                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.510   0.657   0.720 0.793 0.867 0.939                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of Unit                                                                          0.136   0.005   0.005 0.006 0.007 0.008                              Weight                                                                        Cracks and                                                                             C       C       C     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      --    98    98    98                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

                  TABLE 23                                                        ______________________________________                                        Filling Density                                                                        0.70    1.00    1.30  1.60  1.90  2.20                               (g/cc)                                                                        Density relative                                                                       15.5    22.2    28.8  35.5  42.1  48.8                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.43    1.86  2.29  2.72  3.15                               True Density                                                                  Filling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.245   0.247   0.320 0.394 0.468 0.542                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.123   0.244   0.317 0.390 0.464 0.539                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of Unit                                                                          0.122   0.003   0.003 0.004 0.004 0.003                              Weight                                                                        Cracks and                                                                             C       C       C     B     A     A                                  Crazings                                                                      Deformation                                                                            C       C       B     A     A     A                                  Density of                                                                             --      --      --    96    96    96                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

                  TABLE 24                                                        ______________________________________                                        Filling Density                                                                        0.50    0.70    0.90  1.10  1.30  1.50                               (g/cc)                                                                        Density relative                                                                       18.5    25.9    33.3  40.7  48.1  55.6                               to True                                                                       Density (%)                                                                   Filling Density/                                                                       1.00    1.40    1.80  2.20  2.60  3.01                               True Density                                                                  Filling Method                                                                         N       NV      NVP   NVP   NVP   NVP                                Maximum Unit                                                                           0.159   0.172   0.222 0.271 0.319 0.368                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Minimum Unit                                                                           0.100   0.171   0.221 0.270 0.318 0.367                              Weight of                                                                     Green                                                                         Compacts (g)                                                                  Range of Unit                                                                          0.059   0.001   0.001 0.001 0.001 0.001                              Weight                                                                        Cracks and                                                                             C       B       A     A     A     A                                  Crazings                                                                      Deformation                                                                            C       B       B     A     A     A                                  Density of                                                                             --      --      95    95    95    95                                 Sintered                                                                      Compact/                                                                      True                                                                          Density (%)                                                                   ______________________________________                                    

EXAMPLE 19

The fine powders of various materials, whose average particle diameter(μm) was varied, were filled into the same rubber mold as in Example 18by the method NV of Example 16. A guide frame, a vibrator and a pusherwere used for the filling. The filling density is shown in Table 25. Thecompacting (GDP) and sintering were carried out under the sameconditions as in Example 17, except for the Fe--45% Co powder which wascompacted and sintered under the conditions in Example 23, below.

For the comparison purpose, the above fine powders were die-pressed (DP)by using a die, whose dimensions were adjusted so that a green compacthaving the same size as the one formed by the rubber mold was obtained.However, the filling of the fine powder into the die was impossiblebecause the fine powder had a very poor flowability. The coarse powdersshown in Table 25 were therefore naturally filled and then compacted ata pressure of 1.5 t/cm². The sintering was carried out under the sameconditions for the fine powders. The filling density and the density ofsintered compacts are shown in Table 25.

                  TABLE 25                                                        ______________________________________                                                                     Filling                                                                             Density of                                           Particle Compacting                                                                              Density                                                                             Sintered compact                           Materials Diameter Method    (g/cc)                                                                              (%)                                        ______________________________________                                        Fe-0.3 wt % C                                                                           12       GDP       3.40  97                                                   20       GDP       3.65  93                                                   60       DP        3.05  86                                         Fe-2 wt % Si                                                                            12       GDP       3.50  98                                                   75       DP        2.90  87                                         Fe-45 wt % Co                                                                           15       GDP       3.70  94                                                   80       DP        3.10  85                                         Fe-42 wt % Ni                                                                           12       GDP       3.55  98                                                   70       DP        2.95  86                                         Al        10       GDP       1.30  95                                                   80       DP        0.80  85                                         Ti        10       GDP       1.90  96                                                   60       DP        1.50  87                                         ______________________________________                                    

EXAMPLE 20

The rubber mold shown in FIG. 61 was used to produce a green compact inthe form of a screw. The cover 10u and side wall 10s consisted of softrubber (JIS A hardness 40). The powders used were atomized Fe--2 wt % Sipowder (average particle diameter--10 μm, the true density--7.7 g/cc, inTable 26), and the hydrogenated and then decomposed Ti powder (averagediameter--10 um, true density--4.5 g/cc, in Table 27). The former powderwas subjected to compacting at a pressure of 1.2 t/cm² and sinteringtemperature at 1150° C. for 6 hours. The latter powder was subjected tocompacting at a pressure of 1.4 t/cm² and sintering temperature of 1150°C. for 6 hours. The results are shown in Tables 26 and 27.

When each of the two kinds of powder was naturally filled and compacted,the rod of thread were particularly seriously damaged. The screws brokebetween the screw head and the screws. Table 26

                  TABLE 26                                                        ______________________________________                                        Filling Density (g/cc)                                                                       2.4    2.70   3.00 3.30 3.60 3.90                              Density relative                                                                             31.1   35.1   39.0 42.9 46.8 50.6                              to True-Density (%)                                                           Filling Density/                                                                             1.00   1.13   1.25 1.38 1.50 1.63                              True Density                                                                  Filling Method N      NV     NVP  NVP  NVP  NVP                               Maximum Unit Weight                                                                          3.00   3.11   3.45 3.79 4.14 4.47                              of Green Compacts (g)                                                         Minimum Unit Weight                                                                          2.40   3.10   3.44 3.78 4.12 4.45                              of Green Compacts (g)                                                         Range of Unit Weight                                                                         0.60   0.01   0.01 0.01 0.02 0.02                              Cracks and Crazings                                                                          C      C      C    B    A    A                                 Deformation    C      C      B    A    A    A                                 Density of Sintered                                                                          --     --     --   98   98   98                                Compact/True Density (%)                                                      ______________________________________                                    

                  TABLE 27                                                        ______________________________________                                        Filling Density (g/cc)                                                                       1.00   1.25   1.50 1.75 2.00 2.25                              Density relative                                                                             22.2   27.7   33.3 38.8 44.3 49.9                              to True Density (%)                                                           Filling Density/                                                                             1.00   1.25   1.50 1.75 2.00 2.25                              True Density                                                                  Filling Method N      NV     NVP  NVP  NVP  NVP                               Maximum Unit Weight                                                                          1.05   1.09   1.31 1.53 1.74 1.96                              of Green Compacts (g)                                                         Minimum Unit Weight                                                                          0.70   1.08   1.30 1.52 1.73 1.95                              of Green Compacts (g)                                                         Range of Unit Weight                                                                         0.35   0.01   0.01 0.01 0.01 0.01                              Cracks and Crazings                                                                          C      C      C    C    A    A                                 Deformation    C      C      C    B    A    A                                 Density of Sintered                                                                          --     --     --   --   96   96                                Compact/True Density (%)                                                      ______________________________________                                    

EXAMPLE 21

The rubber molds A and B shown in FIG. 62 were used to compact theFe--45 wt % Co fine powder (average particle diameter--12 μm) to afilling density of 3.70 g/cc. The dimensions of the die cavity were30×30×3 mm for every mold. The entire (10u, k) of the rubber mold Aconsisted of soft rubber (hardness 40). The side wall 10s of the rubbermold B consisted of the soft rubber mentioned above, while the otherportions 10u, k consisted of hard rubber (hardness 90). The fine powderwas preliminarily weighed and was then naturally filled in the rubbermolds using a guide frame. Then, the forced filling was carried out byutilizing vibration and pushing.

Compacting was repeated ten times under the compacting pressure of 1.0t/cm². Every green compact produced by using the rubber mold A cracked,while every green compact produced by using the rubber mold B did notcrack and attained excellent shaping.

EXAMPLE 22

The method of Example 20 was carried out for using the rubber moldsshown in FIG. 63.

    ______________________________________                                                 Rubber Mold A                                                                              Rubber Mold B                                           ______________________________________                                        Cover      soft rubber    hard rubber                                                    (JIS A hardness 40)                                                                          (JIS A hardness 80)                                 Side wall  hard rubber    soft rubber                                                    (hardness 80)  (hardness 40)                                       Bottom     soft rubber    hard rubber                                                    (hardness 40)  (hardness 80)                                       ______________________________________                                    

Every green compact produced by using the rubber mold B cracked, whileevery green compact produced by using the rubber mold did not crack andattained excellent shaping.

EXAMPLE 23

The rubber molds shown in FIGS. 64(A) through (C) were used to compactthe atomized aluminum powder (average particle diameter--30 μm) . Rubbermold (A)

Cover--hard rubber (hardness 90)

Side wall--soft rubber (hardness 40)

inner coating (10n)--no Rubber mold (B)

Cover--hard rubber (hardness 80)

Side wall--soft rubber (hardness 40)

inner coating (10n)--Polytetrafluoroethylene Rubber mold (C)

Cover--hard rubber (hardness 80)

Side wall--soft rubber (hardness 40)

inner coating (10n)--soft rubber, in which 40% of MoS₂ is blended (t=1mm)

During the powder compaction using Rubber mold (A), the green compactwas seized by the rubber mold, and the green compact could not beremoved from the rubber mold, even by turning the rubber mold upsidedown and applying pressure of 1.0 kg/cm of pressurized air into therubber mold. No seizure occurred in the cases of Rubber molds B and C atall. The green compacts could easily be removed from the rubber molds byturning upside down the rubber molds and then expanding them, allowingthe compacts to fall out.

EXAMPLE 24

The rubber molds shown in FIGS. 65(A), (B) and (C) were used to compactthe fine Fe--2 wt % Si powder (average particle diameter 12 μm). Thecompacting pressure was 1 t/cm². The generation of cracks in relation tothe material of mandrel was investigated.

Rubber Mold (A)

Outer diameter--33 mm

Inner diameter--24 mm

Height--18 mm

Mandrel m--12 mm in outer diameter and 15 mm in height (at the setting)Rubber Mold (B)

Outer diameter--33 mm

Inner diameter--24 mm

Height--18 mm

Mandrel m--12.5 mm in outer diameter and 7.5 mm in height (at thesetting)

Rubber Mold (A)

Outer diameter--33 mm

Inner diameter--24 mm

Height--18 mm

Mandrel m--eight radially arranged blades, each 1.5 mm

in thickness, 7.5 mm in height

Number of cracks are shown in Table 28.

                  TABLE 28                                                        ______________________________________                                        Hardness of  Rubber Molds                                                     mandrels     (A)          (B)   (C)                                           ______________________________________                                        40 (soft rubber)                                                                           10           10    10                                            90 (hard rubber)                                                                            0            1     2                                            Metal         0            0     0                                            ______________________________________                                    

EXAMPLE 25

High purity Al and high purity Li were blended to provide an alloycomposition of Al--2.84 wt % Li and was then melted in a Ar atmosphere.The melt was atomized by Ar gas to provide the fine powder of Al-Lialloy having average particle diameter of 8 μm. This powder subjected tothe production of green compacts by the circulating type apparatusillustrated in FIG. 39. The rubber mold was a hollow type made of hardurethane resin (hardness 60) and 30 mm in inner diameter and 10 mm inheight. When the entire apparatus was exposed to the ambient air, theignition of the powder so frequently occurred that the powder compactingwas impossible. When the circular die 40 was located in the chamber, inwhich argon gas was filled, the powder compacting became possible.

We claim:
 1. An apparatus for production of a green compact comprising acircuit circulating die assemblies, each of said die assembliescontaining a rubber mold which comprises rubber in at least its sideportion, a high density filling device comprising a feeder for feeding apowder into the rubber molds and a pusher or a vibrator or both avibrator and a pusher; a die press machine configured to impart acompaction force sufficient to produce the green compact to each of saidcirculating die assemblies in succession; and a device for removing thegreen compact from each rubber mold, said high-density filling device,die-press machine and removing device being successively arranged alongthe circuit, wherein each of said circulating die assemblies hassufficient structural integrity to withstand the compactionforce,wherein all structure necessary to withstand the compaction forceis present in said circulating die assemblies.
 2. An apparatus forproduction of a green compact comprising a circuit circulating dieassemblies, each of said die assemblies containing a rubber mold whichcomprises rubber in at least its side portion, a high density fillingdevice comprising a feeder for feeding a powder into the rubber moldsand a vibrator and a pusher or both a vibrator and a pusher at the sameplace as said feeder; a die press machine configured to impart acompaction force sufficient to produce the green compact to each of saidcirculating die assemblies in succession; and a device for removing agreen compact from each rubber mold, said high-density filling device,die-press machine and removing device being successively arranged alongthe circuit, wherein each of said circulating die assemblies hassufficient structural integrity to withstand the compactionforce,wherein all structure necessary to withstand the compaction forceis present in said circulating die assemblies.
 3. An apparatus forproduction a green compact according to claim 2, further comprising amagnetic field generator, said high-density filling device, magneticfield-generator, die-press machine and removing device beingsuccessively arranged along the circuit.
 4. An apparatus for productionof a green compact according to claim 1, 2 or 3, further comprising achamber having inert-gas atmosphere, wherein said circuit is located. 5.An apparatus for production of a green compact according to claim 1, 2,or 3, wherein a die is detachably mounted in the circuit.
 6. Anapparatus. for production of a green compact according to claim 1, 2, or3, further comprising a means for weighing the powder to provide apredetermined weight, said weighing means being arranged on the circuitbefore said high density filling device.
 7. An apparatus for productionof a green compact according to claim 6, further comprising a chamberhaving inert-gas atmosphere, therein in which said circuit is located.8. An apparatus for production of a green compact, according to claim 4,wherein a die is detachably mounted in the circuit.
 9. An apparatus forproduction of a green compact, according to claim 4, further comprisinga means for weighing the powder to provide a predetermined weight, saidweighing means being arranged on the circuit before said high densityfilling device.
 10. An apparatus for production for a green compact,according to claim 9, further comprising a chamber having inert-gasatmosphere, therein in which said circuit is located.
 11. An apparatusfor production of a green compact comprising a circuit circulating dieassemblies, each of said die assemblies containing a rubber mold whichcomprises rubber in at least its side portion, a filling devicecomprising a feeder for feeding a starting material for making greencompacts into the rubber molds and a pusher or a vibrator or both avibrator and a pusher; a die press machine configured to impart acompaction force sufficient to produce the green compact to each of saidcirculating die assemblies containing a rubber mold in succession; and adevice for removing the green compact from each rubber mold, saidfilling device, die-press machine and removing device being successivelyarranged along the circuit, wherein each of said dies has sufficientstructural integrity to withstand the compaction force,wherein allstructure necessary to withstand the compaction force is present in saidcirculating die assemblies.
 12. An apparatus for production of a greencompact according to claim 4, wherein a die is detachably mounted in thecircuit.
 13. An apparatus for production of a green compact according toclaim 4, further comprising a means for weighing the powder to provide apredetermined weight, said weighing means being arranged on the circuitbefore said high density filling device.
 14. An apparatus for productionof a green compact according to claim 13, further comprising a chamberhaving an inert-gas atmosphere therein, said circuit being located insaid chamber.
 15. An apparatus for production of a green compactaccording to claim 1, 2 or 11, wherein said circulating die assembliescomprise a die and a movable stage.
 16. An apparatus for production of agreen compact comprising: a mold supporting means having a configurationof an equiangular polygon, a high-density filling device comprising afeeder for feeding powder into a rubber mold which comprises rubber atleast in its side portion, and one or both of a pusher and a vibrator; adie-press machine; and a device for removing a green compact;wherein atleast one of said high-density filling device, said die-press machineand said device for removing the green compact is located at an apexregion of said equiangular polygon, said apparatus further comprising ameans for transporting the rubber molds in a linear movement betweenadjacent apexes.
 17. An apparatus for production of a green compactcomprising: a mold supporting means having a configuration of anequiangular polygon, a high-density filling device comprising a feederfor feeding powder into a rubber mold which comprises rubber at least inits side portion, and a vibrator along with or instead of said pusher atthe same place as said feeder; a die-press machine; and a device forremoving a green compact;wherein at least one of said high-densityfilling device, said die-press machine and said device for removing thegreen compact is located at an apex region of said equiangular polygon,said apparatus further comprising a means for transporting the rubbermolds in a linear movement between adjacent apexes.
 18. An apparatus forproduction of a green compact according to claims 16 or 17, wherein saidlinear transporting means comprises a rail extending between theadjacent apexes and at least two palettes slidably mounted on rails andsupporting the rubber mold and the die.
 19. An apparatus for productionof a green compact according to claim 18, wherein said palettes comprisea movable stage inserted vertically slidably therein and supporting thedie on its top surface, said movable stage being resiliently supportedby the body of said palettes.
 20. An apparatus for production of a greencompact according to claim 19, wherein a means for resilientlysupporting the movable stage are springs.
 21. An apparatus forproduction of a green compact, according to claim 19, further comprisinga magnetic-field generator.
 22. An apparatus for producing a greencompact, according to claim 19, further comprising a chamber havinginert-gas atmosphere therein.
 23. An apparatus for production of a greencompact, according to claim 20, further comprising a magnetic-fieldgenerator.
 24. An apparatus for producing a green compact, according toclaim 20, further comprising a chamber having inert-gas atmospheretherein.